It's the comparative of gosu.

Gosu is a Korean loan word. In korean its meaning is "skilled" or "dexterous" - literally "top hand"

In gaming terms it's defined as "skilled" or "incredible" player. It's also used as an adjective. Gosuer is the comparative form of that adjective, meaning "more gosu" or "more skilled"
"Spirit_Moon is gosuer than I thought!"
by iopq February 18, 2005
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