Short for the two words "Silly Master." Or, depending on how you use it, it can mean Silly Masturbater. Mostly used while texting.
Ex 1:
"Laughing my fucking ass off, you're a silmaster at this game."

Ex 2: (Said by an Australian, or a British person.)
"Oi, get oveh he'e ye silmasta'"
by NoobHammer May 11, 2021
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