In English, the first usage of "crescent" (up to around 1600) was to indicate the waxing moon, anywhere from new to full. The waning moon was "decrescent". Luna crescens and luna decrescens, in Latin.
Somewhere in the late 1500s, though, someone rehooked the meaning to the shape we now call a "crescent".
I'd guess the French must have gone through a similar evolution: it would be fascinating to explore how both languages ended up making the same switch.

Grant Hutchison