Low-class vocabulary lesson
These days, the preferred Japanese entertainment (and "entertainment") industry slang for a large-breasted woman is 巨乳, kyonyuu, literally "giant breasts". The antonym is 微乳, binyuu, with a meaning you can probably guess, but some prefer the term 美乳, binyuu -- same pronunciation, but it means "beautiful breasts".
These are all respectably kanjified terms, although I doubt they have any basis in actual Chinese vocabulary. However, there is an older slang term for the amply endowed, apparently dating back to the eighties: ぼいん, boin, which seems to be onomatopoeic for the mental impression such a person makes. (A boi-oi-oing sound effect is not uncommon in cartoons to accompany the sudden appearance of a sexy female character, and ぼいん is also the sound of being punched, or bouncing.)
OK, so what's the opposite of ぼいん? ないん, nain. An extremely cruel blend of the general sound outlines of boin with the negating word nai. Ouch.
UPDATE! And in Korean...
Duncan:
Hey, it's my term to put up a comment about Chinese again.
All the Kanji words you had in the post would "pass" as Chinese words, with 微乳 sounding the most "weird". It'll probably not come in naturally in that form in normal conversation.
巨乳 works in Chinese, an alternative is 豪乳。
In Chinese, 乳 refers specifically to "mammeries", to refer to chest / breast alone, we tend to use 胸. So in colloquial terms, 大胸 and 細胸 for big-breasted / small-breasted.
As for ぼいん, I think the equivalent (at least in colloquial Cantonese) would be 大波