like mad li·ke·mad uncommon adverb 1. with great speed or effort or intensity “drove like crazy” “worked like hell to get the job done” “ran like sin for the storm cellar” “work like thunder” “fought like the devil” Synonymslike helllike madlike crazylike sinlike thunderlike the devil WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.