'Bitter' in the Bible

All through the life of Saul there was bitter war against the Philistines; and whenever Saul saw any strong man or any good fighting man, he kept him near himself.

And everyone who was in trouble, and everyone who was in debt, and everyone who was bitter in soul, came together to him, and he became captain over them: about four hundred men were joined to him.

And David was greatly troubled; for the people were talking of stoning him, because their hearts were bitter, every man sorrowing for his sons and his daughters: but David made himself strong in the Lord his God.