'Bitter' in the Bible

Just consider and meditate on Him who endured from sinners such bitter hostility against Himself [consider it all in comparison with your trials], so that you will not grow weary and lose heart.

See to it that no one falls short of God’s grace; that no root of resentment springs up and causes trouble, and by it many be defiled;

For you know that later on, when he wanted [to regain title to] his inheritance of the blessing, he was rejected, for he found no opportunity for repentance [there was no way to repair what he had done, no chance to recall the choice he had made], even though he sought for it with [bitter] tears.