Villainous means wicked in the manner of a story's villain. A villainous grin, villainous behaviour, look villainous.
It is theatrical rather than serious, which is why it suits moustaches and cackles more than real crime. The villain was originally a farm labourer, and the word's descent from that to wickedness is a lesson in how the powerful describe the poor.
1adjectivevillainousWicked in the manner of a story's villain.
“The actor with the long black moustache played the villainous landlord.”
villainous is a quality.
Old French vileneus comes from vilain, a peasant, from Latin villa, a farm.
Old French
vileneus
Middle English
vileinous
English, today
villainous
From Middle English vileinous, from Old French vileneus. by surface analysis, villain + -ous.
Etymology from Wiktionary, CC BY-SA