appall (v.)
also appal, early 14c., "to fade;" c. 1400, "to grow pale," from Old French apalir "become or make pale," from a- "to" (see ad-) + palir "grow pale," from Latin pallere "to be pale" (from PIE root *pel- (1) "pale"). Transitive meaning "cause dismay or shock," is 1530s. Related: Appalled; appalling.