Bitterness (Exodus 1:14; Ruth 1:20; Jeremiah 9:15) is symbolical of affliction, misery, and servitude. It was for this reason that, in the celebration of the Passover, the servitude of the Israelites in Egypt was typically represented by bitter herbs.
The gall of bitterness (Acts 8:23) describes a state of extreme wickedness, highly offensive to God, and hurtful to others.
A root of bitterness (Hebrews 12:15) expresses a wicked or scandalous person, or any dangerous sin leading to apostasy.