Simmer with anger (4)
'simmer with anger' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for seethe that I've seen before include "Boil turbulently" , "Barely contain one's anger" , "Appear as if boiling" , "become agitated" , "Ferment, sizzle" .)
(Other definitions for stew that I've seen before include "A hole, a fix" , "Slow cooked meat dish" , "Simmer" , "Cook; worry" , "Meat and veg dish" .)