From WordNet (r) 2.0 (August 2003) [wn]:
tosser
n 1: terms of abuse for a masturbator [syn: jerk-off, wanker]
2: someone who throws lightly (as with the palm upward)
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Tosser \Toss"er\, n.
One who tosses. --J. Fletcher.
[1913 Webster]