or tee-shirt, tee shirt
a lightweight, usually knitted, pullover shirt, close-fitting and with a round neckline and short sleeves, worn as an undershirt or outer garment.
Origin of T-shirt
First recorded in 1940–45; named from its shape
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a lightweight simple garment for the upper body, usually short-sleeved
Word Origin for T-shirt
so called because of its shape
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
1920, in reference to the shape it makes when laid out flat.
Online Etymology Dictionary, © 2010 Douglas Harper