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2.
A negative adjective describing a person, whom is usually lumpy. It can also be used as a noun.
Did you see that lumpster woman who exited the elevator?

That lumpster just fell down the stairs.
by Lumberjack March 22, 2003
 
1.
lumpster can also be used affectionately as a nickname as an alternative to lumpy
One friend says to the other "Hey Lumpster, don't you have a graphic design project due tomorrow?"
by Lumpster December 13, 2004