to have a partial erection of the penis
i saw my grandma naked but i wasn't sure if i liked it or not so i had a semi chub.
by uperv13 May 05, 2010
A boner in an early stage of development. It is no longer flacid, but not quite erect yet.
Dude "Hey Ben did you see Lupitas ass during swimming today" Ben "Hell yeah, she gave me a little bit of semi-chub"
by Martin slasher07 December 14, 2011