French word certainement comes from French -ment, French certaine

Detailed word origin of certainement

Dictionary entry	Language	Definition
-ment	French (fra)	Used to form adverbs (from the feminine form of an adjective), most of the time equivalent to the English -wise, -ly. Used to form nouns from verbs, usually of action or state resulting of them. Equivalent to the English -ment.
certaine	French (fra)
certainement	French (fra)	Certainly (with certainty, without doubt).

Words with the same origin as certainement