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the fat on the underside of someones arm.
"Dude, did you see Katie last night?"
"Yea man!! When we were doing the YMCA last night her funderside almost hit me in the face!!"
"Yea, dude. She got fat."
by fatpeoplesuckalotdoingtheymca October 08, 2009

Words related to funderside

arms chunky fat weight ymca