Where does “lactate” come from?

lactate (French) comes from French -ate, from Latin -ātus, from Proto-Italic -ātos, from Proto-Indo-European -éh₂tos.

Ancestry of “lactate”, step by step

Step	Language	Word	Meaning
1	French	-ate	-ate
2	Latin	-ātus	—
3	Proto-Italic	-ātos	—
4	Proto-Indo-European	-éh₂tos	—