noun
small bust; small breasts
Wasei-eigo from French 'petite' and English 'bust'. Used in fashion and body-type descriptions, often with a neutral or slightly euphemistic tone.
wasei (Japanese coinage from French), from petite · wasei-eigo (Japanese-coined English), from bust
彼女はプチバストなので、小さいサイズのブラを探している。
She has a small bust, so she's looking for a smaller-sized bra.
プチバスト向けのファッション特集が雑誌に載っていた。
There was a fashion feature for small-busted women in the magazine.