Crossword Genius

Boil vigorously (6)

Ross

I believe the answer is:

seethe

(Other definitions for seethe that I've seen before include "become agitated" , "Feel intense rage" , "Surge or foam, as if boiling" , "Boil; fume with suppressed rage" , "Boil or become very angry" .)

I've seen this clue in The Guardian.
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