Source : Webster's Revised Unabridged Dictionary (1913)

Cornstarch \Corn"starch`\ (-st[aum]rch`), n.
   Starch made from Indian corn, esp. a fine white flour used
   for puddings, etc.

Source : WordNet®

cornstarch
     n : starch prepared from the grains of corn; used in cooking as
         a thickener [syn: {cornflour}]