ボインボイン

noun, noun which may take the genitive case particle 'no'

big breasts; big boobs

Slangy onomatopoeic term for large breasts, evoking a bouncing motion. Casual and somewhat vulgar.

See also: ぼいん

• 彼かの女じょはボインボインで、よくからかわれる。

  She has big boobs and often gets teased about it.

• あのグラビアアイドルはボインボインだ。

  That gravure idol is really busty.

noun

boing-boing

Onomatopoeia for a springy, bouncing sound or motion, like a spring or large breasts bouncing. Often used in manga or casual speech.

• バネがボインボインと跳はねる。

  The spring bounces with a boing-boing sound.