Tab1  —n. 1 small flap or strip of material attached for grasping, fastening, or hanging up, or for identification. 2 us colloq. Bill (picked up the tab). 3  distinguishing mark on a staff officer's collar. —v. (-bb-) provide with a tab or tabs.  keep tabs (or a tab) on colloq. 1 keep account of. 2 have under observation or in check. [probably dial.]