from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A short-sleeved, collarless undershirt.
- n. An outer shirt of a design similar to the T-shirt.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A lightweight shirt without buttons, with short sleeves and no collar. Often made of cotton and frequently bears a picture or slogan.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a close-fitting pullover shirt
Perhaps from its being shaped like the letter T when spread out.(American Heritage® Dictionary of the English Language, Fourth Edition)
From its shape. (Wiktionary)