I find dictionary definitions quite usful and although I think some cooking-related words may have a different meaning depending on the region... this is how I learnt them in Grandma's kitchen:
Sazonar: usually to add spices, salt and pepper (in this case, it's a synonym of "condimentar"); but in Mexico it can also be to cook something with a low or medium flame until flavor of spices you have just added is concentrated.
Adobar: to cook meat in a (very) spiced sauce. It's usually marinated and then cooked in the same sauce.
Aderezar: I have only heard it for salads, yes. "Aliñar" is a synonym, although it's not used in Mexico.
Marinar: to put meat in a liquid preparation with spices for some time before cooking. The marinating mixture is usually discarded afterwards.