embitters

third-person singular simple present indicative of embitter

(archaic, transitive) To cause (something) to be or taste bitter; to bitter.
(figuratively, transitive) To cause (a positive quality such as happiness, or a thing such as an activity or one's life) to become less good or pleasurable; also, to make (a negative quality, or thing such as a disagreement) worse or more unpleasant.
(figuratively, transitive) To cause (someone or their feelings) to become more angry, resentful, or unfriendly; to envenom.