cook slowly and for a long time in liquid(verb.change)
Example: Stew the vegetables in wine.
source: wordnet30
To boil slowly, or with the simmering or moderate heat; to seethe; to cook in a little liquid, over a gentle fire, without boiling; as, to stew meat; to stew oysters; to stew apples.(verb)
source: webster1913
To be seethed or cooked in a slow, gentle manner, or in heat and moisture.(verb)