Easton's Bible Dictionary
Bitterness is symbolical of affliction, misery, and servitude (Exodus 1:14; Ruth 1:20; Jeremiah 9:15). The Chaldeans are called the "bitter and hasty nation" (Habakkuk 1:6). The "gall of bitterness" expresses a state of great wickedness (Acts 8:23). A "root of bitterness" is a wicked person or a dangerous sin (Hebrews 12:15).
The Passover was to be eaten with "bitter herbs" (Exodus 12:8; Numbers 9:11). The kind of herbs so designated is not known. Probably they were any bitter herbs obtainable at the place and time when the Passover was celebrated. They represented the severity of the servitude under which the people groaned; and have been regarded also as typical of the sufferings of Christ.
Noah Webster's New International Dictionary of the English Language
1. (n.) AA turn of the cable which is round the bitts.
2. (v. t.) Having a peculiar, acrid, biting taste, like that of wormwood or an infusion of hops; as, a bitter medicine; bitter as aloes.
3. (v. t.) Causing pain or smart; piercing; painful; sharp; severe; as, a bitter cold day.
4. (v. t.) Causing, or fitted to cause, pain or distress to the mind; calamitous; poignant.
5. (v. t.) Characterized by sharpness, severity, or cruelty; harsh; stern; virulent; as, bitter reproach.
6. (v. t.) Mournful; sad; distressing; painful; pitiable.
7. (n.) Any substance that is bitter. See Bitters.
8. (v. t.) To make bitter.