T-shirt is a shorter - if not, an abbreivation of 'Tee Shirt'. I assume that the 'Tee' in 'Tee Shirt' is simply a name given to the type of garment worn (a light garment worn over an undershirt, but under a jacket or coat)

Good question! I always thought it was because of the shirt's T shape. Any other theories?

Yea... i suppose its coz tee-shirt, but from time to time / during the time tee-shirt not written like that anymore, just make it simple T-shirt heheh... ; )

it is Tee-shirt

from wikipedia: http://goo.gl/oUOZ 17世纪中，美国安那波利斯港口茶叶码头工人穿一种短袖衫，据说这就是T恤的最初发源，由于TEA和TEE谐音，故有TEE（TEA）-SHIRT一说，后简称T-SHIRT或者TEE.19世纪后期，T-SHIRT逐渐成为英美海军的内衣制服。随着针织工业的兴起，T-shirt作为内衣开始被广泛接受。