Sweater \Sweat"er\, n.

1. One who sweats.

2. One who, or that which, causes to sweat; as:
   (a) A sudorific.
   (b) A woolen jacket or jersey worn by athletes.
   (c) An employer who oppresses his workmen by paying low wages. [Slang]

Source: Webster's Revised Unabridged Dictionary (1913)