German does not have an adverb suffix, so I would guess, there was a time when English had none as well; however, I could not find anything on the Internet about it. If I was right, does someone know when and from which language English got its adverb suffix? My guess would usually be Latin or French, but as far as I know, Latin usually uses -e, and French has -ment, so I am at my wits' end. Does -ly derive from Vulgar Latin? Is it even Celtic, or still (ancient) German after all? If anyone knows more, I will be very interested in learning more.