Boil with anger (6)
I believe the answer is:
seethe
'boil with anger' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seethe that I've seen before include "Bubble gently like boiling water" , "Surge or foam, as if boiling" , "Be filled with intense but unexpressed anger" , "foam at the mouth" , "become agitated" .)