Heinous means wicked in the extreme. A heinous crime, heinous acts, the most heinous offences.
It belongs to the law and to serious journalism and it is reserved for the worst — a heinous crime is not merely a bad one. It is pronounced to rhyme with famous rather than with genius, which catches a great many people out.
1adjectiveheinousWicked in the extreme.
“Poisoning the town's water supply would be a heinous act.”
heinous is a quality.
Old French haineus comes from hair, to hate. What is heinous is what deserves hatred.
Proto-Indo-European
*keh₂d-
Frankish
*hattjan — to hate
Old French
haïr
Anglo-Norman
hainous
Middle English
heynous
English, today
heinous
Built from
From Middle English heynous, from Anglo-Norman hainous, heinous (compare French haineux) from Old French haïr, hadir (“to hate”) (compare Old French enhadir (“to become filled with hate”)), from Frankish hattjan (“to hate”) (compare Middle English hetien). More at hate. The fluctuation between pronunciations with and is old; the former reflects adoption of an unmonophthongised pronunciation of Old French -ai-, while the latter reflects a monophthongised form.
Etymology from Wiktionary, CC BY-SA