Letter-words

Some objects look like a certain alphabetical letter. e.g. an A-line skirt is tight-fitting and looks like the letter A.

T
T-bone steak (has a T shaped bone)
T-junction (road junction shaped like the letter T)
T-shirt (a T shaped short-sleeved vest)

U
U-turn (a 180 degree turn)
U-bend (waste pipe shaped like a u)

V
V-formation (airplanes flying in the shape of a V)
V-neck (sweater, shirt or vest with a V shaped neckline)

Other words consist of a single letter in the first part which stands for a word.
A-bomb (atom)
E-mail (electronic)
X-ray (electromagnetic radiation)