undershirt

An upper undergarment, typically having short or no sleeves, worn next to the skin under a shirt.

A shirt or similar garment, as of woolen, worn under a shirt and next to the skin.

A shirt worn next the skin, under another shirt; — called also undervest.

an upper undergarment with no collar, and with short or no sleeves, worn next to the skin under a shirt; a singlet or (British) a vest

a collarless men’s undergarment for the upper part of the body