To be prejudice against some one of a certain mass or weight. Like being sexist or racist
Kassandra: OMG that girl is so fat! I could never hang out with someone like that.

Railey: sshhh Kass ur being so massist!
by timmiehoe January 19, 2009
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a person who discriminates people because of weight.
Some people think the idea of fat people having to pay more for a plane ticket is massist.
by julia3230632 September 15, 2009
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