Yes: moult (Trésor de la langue française, Dictionaire de l'Académie française (latest editions, previous editions didn't list this word), Littré). This word disappeared from common usage in the 16th century in favor of beaucoup.
It may have survived in some regional usage, but other than that people wouldn't use it naturally. I think that a non-negligible proportion of native speakers wouldn't recognize it at all. (I even suspect that more people would recognize [mɔlto] than [mult], let alone the historical pronunciation [mu].)
Historically moult was an adverb meaning beaucoup (a lot), but in modern (post-16th century) literary usage it's mostly used as an adjective meaning beaucoup de (a lot of).
Other derivatives of multum have survived in French through the prefix multi-, which is very common.