28 synonyms for insufficient such as in short supply, at a premium, and deficient. Insufficient is an adjective, and its antonyms are sufficient and adequate.
At a premium, deficient, exiguous, in short supply, inadequate, incomplete, lacking, limited, meagre, measly, not enough, paltry, pathetic, piddling, poor, restricted, scant, scanty, scarce, short, sketchy, skimpy, sparse, too few, too little, too small, and wanting.