underbust noun 2adjective 1forms 1 noun2 •The circumference of a woman's chest, measured under the breasts.You can measure your underbust and overbust to get an idea of bra size, but it's still just a guideline. — 2015 •A corset that begins just under the breasts and extends down to the hips. adjective1 •Below the bust. formsunderbusts
