A radio comic-song from 1968. A nationally-circulated joke about breasts in a baby’s mouth. A new word, boin, lifting off from the song and into the everyday Japanese-language vocabulary of the next decade. Boin is a strangely-specific case in the postwar Japanese language: a word for full and bouncy breasts that did not come out of medical-vocabulary, did not come out of business-or-industry-vocabulary, but came out of a popular-comic-song that the country happened to be paying attention to in a particular year.

Overview

Boin (Japanese: ボイン or ぼいん, boin; English working translations: big and bouncy breasts, vintage Japanese vernacular for full breasts; the term has no native-English equivalent) is a Japanese vernacular-and-comedic-onomatopoeic term for full, bouncy, voluminous breasts. The term entered the Japanese language in 1968 with the comic song Boin wa Akachan no… (“Boin is the baby’s…”) performed by the rakugo storyteller Tsuki no Ya Enkyo (later Tachibanaya Enzō, Eighth-generation), and it spread rapidly through television, radio, and weekly-magazines into the wider Japanese-language vocabulary of the 1970s and 1980s.

The term’s distinctive feature in contemporary Japanese is its vintage register. Younger speakers of Japanese, working with the contemporary vocabulary of kyonyū (large breasts) and bakunyū (extreme breasts), tend to use boin only in deliberately-vintage or comic registers. Older speakers — those who came of age in the 1970s and 1980s — used boin as a routine vocabulary-item, and the term remains current in their generation’s vernacular. The term’s generational-register is one of its distinctive contemporary features.

In international adult-vocabulary contexts, boin circulates as a Japanese-loan term identifying the specifically-Japanese-vintage register of the breast-vocabulary, distinct from the more-current kyonyū and bakunyū terms that have travelled internationally as the standard contemporary Japanese vocabulary.

Etymology

The term boin (ボイン) is structured as a Japanese sound-symbolic-onomatopoeic compound: “ボ” (bo, a heavy bilabial nasal-stop initial) + “イン” (in, a final-nasal sound suggesting bounce-and-spring). The structure follows the broader Japanese sound-symbolism logic in which the bilabial bo- initial is associated with weight, mass, and substance, and the -in final is associated with springiness and bounce. The combined sound describes, through its phonological structure, the corresponding physical-property: voluminous and bouncy.

This kind of compound — onomatopoeic representation of physical-property through sound — has many parallels in Japanese: purin-purin (springy), purun-purun (similar), tapu-tapu (soft and yielding), muchi-muchi (full and tightly-curved). Each onomatopoeic-compound describes through its sound-structure the corresponding physical-property, and the Japanese language’s broader sound-symbolic vocabulary has many examples of this descriptive logic. Boin’s onomatopoeic-pattern is one of many in the broader vocabulary, and its specific sound-physical-property correspondence reads naturally to the Japanese ear.

The proximate origin of boin in its current sense is the 1968 comic song. Some informal etymological accounts cite earlier Kansai-region dialect-or-comedian-vocabulary use of the word in similar senses, but the documented 1968-origin in the song is the consolidating-and-popularising moment. Before 1968, the term existed only in scattered-and-localised use; after 1968, it was a national-vocabulary item.

History

1968: the origin and the song

The proximate-origin of contemporary boin is the comic song Boin wa Akachan no… (“Boin is the baby’s…”), performed by the rakugo storyteller Tsuki no Ya Enkyo in 1968. The song’s central conceit is the framing of breasts as the baby’s food, with the lyric “boin wa akachan no… tabemono na no yo ne…” (“boin is the baby’s… food, you know…”). The comic register lifts the lyric out of the medical-or-clinical vocabulary that postwar Japanese-mainstream-broadcasting would otherwise have required, and the comic register’s success carried the song into national-broadcast circulation.

The song’s repeated use of the word boin normalised the term as a vocabulary-item. Within a year or two of the song’s release, the word had entered general Japanese-language usage, with the comic register of its origin still readable to Japanese-speakers but the term itself functioning as a standard vocabulary-item. The term’s success-in-spreading owed much to the comic-and-affectionate register it occupied: where the medical-or-anatomical word kyonyū would have been too clinical, and where a more direct-vernacular term would have been too coarse for general broadcast, boin sat in a middle-register that was both informal-friendly-and-broadcast-acceptable.

1970s–1980s: vocabulary-stabilisation

Through the 1970s and 1980s, boin became a standard component of Japanese-vernacular vocabulary. Weekly-magazine gravure features used the term in their headline-and-caption vocabulary, sports-newspaper sex-and-women’s-feature pages used it routinely, the rakugo-and-stage comedy tradition used it in its standard-comedy vocabulary, and the broader television-and-radio entertainment context used the term extensively. The middle-register-and-comic-affectionate quality of the term made it well-suited to the wide range of media-context in which it circulated.

In this period the term was usable in mainstream-broadcasting context where more-clinical or more-direct vocabulary would have been awkward. The term’s middle-ground position in the vocabulary of breast-description made it functionally-valuable for a wide range of vernacular-and-mass-media uses, and the term’s currency through the period was correspondingly broad.

1980s onward: the kyonyū-and-bakunyū-replacement

In the late 1980s and early 1990s, the AV-industry’s emergence and the corresponding development of more-specifically-pornographic vocabulary brought the terms kyonyū and bakunyū into wider circulation. These terms were more clinical-and-categorical — they functioned as size-classification rather than as general-vernacular-affectionate vocabulary — and they suited the AV-industry’s catalogue-and-tag-based commerce-vocabulary better than the comic-affectionate boin did.

Through the 1990s, the AV-industry-driven kyonyū / bakunyū terminology became the standard adult-content-industry vocabulary, with boin receding to the more-vernacular-and-vintage register. The contemporary distribution between the registers has stabilised: kyonyū and bakunyū operate in adult-content-and-categorical contexts, boin operates in vernacular-and-affectionate-and-vintage contexts.

Contemporary register

In contemporary Japanese, boin operates primarily in the Shōwa-era vintage register — the register of speakers who came of age in the 1970s and 1980s, who use the term as part of their routine vocabulary. Younger speakers tend to know the term but use it only in deliberately-vintage contexts, comedy registers, or when speaking with older interlocutors. The term remains current in the vernacular of jukujo (mature-woman) AV genres, in retro-and-vintage adult-content production, and in the broader comedic-vocabulary register where its 1968-origin is still readable.

Uses and registers

The boin category has a particular set of register-distinctions from the more-current kyonyū and bakunyū vocabularies.

Comic-affectionate vs. clinical-categorical. Boin operates in a comic-affectionate register; kyonyū and bakunyū operate in a clinical-categorical register. Boin can be used in friendly-banter contexts and in contexts where the speaker wants to maintain a light-and-comic register; kyonyū and bakunyū are more-suitable for catalogue-and-categorical contexts.

Generational-register. Boin reads as Shōwa-era and vintage; kyonyū and bakunyū read as contemporary. The use of boin by a younger speaker is therefore a deliberate-register-choice, and is frequently used for comic-or-retro effect. The use of kyonyū / bakunyū by an older speaker is also possible but less remarkable.

Size and quality scope. Boin covers a slightly different size-and-quality range than kyonyū / bakunyū. Kyonyū is a size-classification (large breasts); bakunyū is an extreme-size-classification (extreme breasts); boin describes the breast’s bouncy-and-substantial-quality without committing to a precise size-classification. Boin therefore covers approximately E-cup through G-and-larger sizes, with the quality-of-bounciness rather than the size-of-volume as its primary referent.

Derivatives

A small number of boin-derivatives are recognised in the broader Japanese vernacular.

• Boi~n: stretched-out bouncy register, with the lengthening of the second sound emphasising the bounce.
• Boin-boin: repetition emphasising sustained-bouncing motion, a standard manga-onomatopoeia for the bounce-of-breasts in motion.
• Kyodai-boin (literally “giant-boin”): emphasised-extreme variant, approximately equivalent to bakunyū.
• Boin-aidoru (boin-idol): the 1970s-and-1980s celebrity-vocabulary for full-figured popular-entertainment performers, particularly the Playmate-tradition of the period.

Cultural references

Boin wa Akachan no… (Tsuki no Ya Enkyo, 1968) is the term’s origin-point and the song’s text remains a referent for the term’s etymology in standard Japanese-language reference works. The song’s broadcast-and-distribution-history through the 1968 entertainment-context is the documented-origin of the term’s national-vocabulary spread.

The term’s circulation through the 1970s and 1980s overlapped with the bodikon (body-conscious) fashion of the late-1980s, and the corresponding boin-and-bodikon visual-and-vocabulary register characterises a particular slice of late-Shōwa popular-culture. The combination of full-figure breast-presentation and tight-fitting body-conscious clothing produced a recognisable visual-register that the vocabulary of boin helped to anchor.

Manga of the 1970s and 1980s — Harenchi Gakuen, Macaroni Hourenso, and the broader shōnen-and-seinen-comic-tradition of the period — used boin extensively in dialogue-and-narration. Anime carried the term through into the 1980s — Urusei Yatsura’s Lum Invader is one of the period’s recognisable boin-coded heroines — and the term remained a routine vocabulary-item through the AV-genre’s emergence in the 1980s and the gradual transition to the kyonyū / bakunyū vocabulary in subsequent decades.

Related Terms

• Oppai (breasts)
• Kyonyū (large breasts)
• Bakunyū (extreme breasts)
• Tarechichi (sagging breasts)
• Bodikon (body-conscious fashion)