noun
underboob
Slang term for the underside of the breasts, often used in fashion or erotic contexts. Vulgar and casual.
その水着は下パイがチラ見えするデザインだ。
That swimsuit has a design where the underboob peeks out.
下パイを見せるとセクシーすぎるかも。
Showing underboob might be too sexy.