beat·er 
(bētər)
(bētər)n.
1. One that beats, especially a device for beating: a carpet beater.
2. A person who drives wild game from under cover for a hunter.
3. Offensive Slang A tight-fitting, white sleeveless undershirt.
4. Informal An old, dilapidated automobile.
[Sense 3, short for WIFEBEATER.]