underbum

== English == === Etymology === From under- +‎ bum, by analogy with underboob. === Pronunciation === === Noun === underbum (plural underbums) (UK, slang) The lower part of the buttocks, as revealed by certain clothing such as skimpy shorts. For more quotations using this term, see Citations:underbum. ==== Synonyms ==== underbutt (North America)