Inadequate, too little, too small, poor, scanty, sparse, in short supply, lacking, paltry, skimpy, incomplete, limited, pathetic, exiguous, not enough, too few, deficient, scant, scarce, short, at a premium, wanting, meagre, sketchy, restricted, measly, and piddling.
Example Sentences of Insufficient
The evidence was deemed insufficient for conviction.
His explanation was insufficient to convince me.