Is it ensure, insure, or assure?
late 14c., schrylle "high-pitched, piercing" (of the voice), probably related to Old English scralletan "to sound loudly" and of imitative origin (cf. Low German schrell, German schrill "piercing, shrill"). Related: Shrillness; shrilly (adv.).
"to sound shrilly," c.1300, imitative (see shrill (adj.). Related: Shrilled; shrilling.