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1.
1. One who will one at all costs, using trickery if necessary.
2. A trickster.
That schister tricked me out of that win!
by The Raven January 25, 2005
 
2.
An alternative for "shit" in expletives.

Extremely effective in a Dublin accent - "shoyster!"
"Ah schiester! The fuckin' wheel came off!"
by Sean Tracey May 01, 2005