It is not often that you see a PIE word spreading to Hittite and Welsh. Here is the word for you. From Online Etymology Dictionary:
"an opinion of private men different from that of the catholick and orthodox church" [Johnson], c.1200, from Old French heresie (12c.), from Latin hæresis, "school of thought, philosophical sect," used by Christian writers for "unorthodox sect or doctrine," from Greek hairesis "a taking or choosing, a choice," from haireisthai "take, seize," middle voice of hairein "to choose," of unknown origin, perhaps from PIE *ser- "to seize" (cf. Hittite šaru "booty," Welsh herw "booty").