you marinate (verb) something in a marinade (noun).

which is what Collins dictionary says....

but the OED says....

marinade v

Origin: A variant or alteration of another lexical item. Etymon: marinate v.
Etymology: Either a variant of marinate v. after marinade n., or directly < marinade n. Compare earlier marinading n., and marinado v.(Show Less)

with an example from 1727!1727 R. Bradley Chomel's Dictionaire Oeconomique (Dublin ed.) at Breast To Marinade a Breast of Veal; cut it into great Slices, marinade them in Vinegar [etc.].

and also give marinate, so it looks like everybody is right

which is a happy ending!