Marinade is a liquid mixture (usually vinegar, oil, and herbs) in which meat is soaked before cooking. Marinate is the corresponding verb (i.e., to soak in marinade). The noun marinade has been mistakenly used in place of the verb marinate so often and for so long that many dictionaries now list marinade as a variant of marinate. Still, there is no reason not to keep the words separate.
Make the marinade by mixing together all the ingredients for it. [Telegraph]
A year later he started making beef jerky using a teriyaki marinade. [CNN]
Toss the chicken with the marinade. Marinate the chicken, covered and refrigerated, at least 2 hours. [Los Angeles Times]
Their factory produces marinated and plain tofu, as well as vegetarian sausages, balls and mince. [Stuff.co.nz]