'Bitterness' in the Bible

whose mouth is full of cursing and bitterness.

All bitterness, and rage, and wrath, and clamor, and abusive speech, must be removed from you, together with all wickedness.

Take care [that] no one falls short of the grace of God; [that] no one growing up [like] a root of bitterness causes trouble, and by it many become defiled;