Longman Dictionary of Contemporary English
Wiktionary
a. (context idiomatic of a girl or woman English) Having a flat chest; having small breasts. alt. (context idiomatic of a girl or woman English) Having a flat chest; having small breasts.
Usage examples of "flat-chested".
She was flat-chested, though an appealing suppleness compensated for her lack of amplitude, and she had a charming feminine delicateness most apparent in her small bones, slender arms, and swanlike neck.
But Vardia Diplo 1261 was the same underneath, anyway: looked twelve, was flat-chested, probably neutered, since there was some pelvic width.
There were fat redheads and skinny redheads, tall ones and short ones, busty ones and flat-chested ones, hippy ones and straight ones, flaming redheads and auburn redheads, natural orange redheads and bleached scarlet redheads, and each and every one of them wanted to see Dave Raskin about this job of modeling women’s dresses in the swank Culver Avenue showroom.
And the best thing about it was that he wouldn't have to take it up with the deacons, or with the Ladies' Aid (an organization which apparently only attracted two types of women - fat slobs with boobs the size of barrels and skinny-assed, flat-chested sluts like Pamela Sargent, with her fake ivory cigarette holder and her raspy smoker's cough), or with the few well-to-do members of his congregation .