Here we have two cooking terms which look oh-so-similar – but one is a noun and one is a verb!
A marinade is a mixture of oils, spices and vinegar in which we soak meat, fish or other proteins such as quorn or tofu, so that they soak up the flavours.
To marinate is to soak such items in such a mixture.
But wait: what’s this? The dictionary also has a verb, to marinade, which means … to marinade.
So you can marinate or marinade your slab of tofu or your fish, but you can only soak them in a marinade.