French word prometteur comes from French -eur, French promettre ((intransitive) to be promising, to be hopeful.. To promise.)

Detailed word origin of prometteur

Dictionary entry	Language	Definition
-eur	French (fra)	Used to form abstract nouns from adjectives; -ness.. Used to form agent nouns from verbs.
promettre	French (fra)	(intransitive) to be promising, to be hopeful.. To promise.
prometteur	French (fra)	Promising Someone who makes false promises.

Words with the same origin as prometteur