French word ennuyeux comes from French ennui, French -eux (-ous, -y.), Old French enuieus

Detailed word origin of ennuyeux

Dictionary entry	Language	Definition
ennui	French (fra)	(uncountable) Boredom; lassitude.. (uncountable) Trouble, issue, annoyance.
-eux	French (fra)	-ous, -y.
enuieus	Old French (fro)
ennuyeux	French (fra)	Annoying. Dull, boring, tedious, tiresome, monotonous.

Words with the same origin as ennuyeux