Meaning

adjective extremely wicked, deeply criminal

originFrom Middle English hainous, from Old French haïneus (compare French haineux) from haïr (“to hate”), hadir (“to hate”) (compare Old French en-hadir (“to become filled with hate”)), from Frankish *hattjan (“to hate”) (compare Middle English hetien). More at hate. The fluctuation between pronunciations with /eɪ/ and /iː/ is old; the former reflects adoption of an unmonophthongised pronunciation of…

Etymology from Wiktionary, CC BY-SA 3.0