Cook slowly in liquid (4)
'cook slowly in liquid' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stew that I've seen before include "State of mental agitation (informal)" , "A hole, a fix" , "Cook slowly and for a long time in liquid" , "Dish of meat and mixed vegetables" , "Boil slowly" .)
(Other definitions for braise that I've seen before include "Cook or stew slowly" , "Fry then stew slowly" , "Fry then stew, eg, steak" , "Cook slowly with little water in closed container" , "Cook slowly with little liquid in closed container" .)