undershirt - Wiktionary, the free dictionary
From Wiktionary, the free dictionary

undershirt (plural undershirts)
- (fashion) An undergarment worn beneath a shirt, often collarless and sleeveless.
2009, Peter Jungk, Crossing the Hudson, page 10:
An undershirt absorbs moisture from your body and equalizes your body temperature.
As a rather generic term, undershirt is more often used in reference to male clothing, while female equivalents employ more specialized terminology.
- singlet, wifebeater (slang, men); vest (UK); see also underbodice (female equivalents)