1 definition found diddly-squat - WordNet (r) 2.1 (2005) : diddly-squat n 1: a small worthless amount; "you don't know jack" [syn: jack, doodly-squat, diddly-squat, diddlysquat, diddly-shit, diddlyshit, diddly, diddley, squat, shit]