Verses with the word bitterness in the New Testament (4 verses):

Acts 8:23
For I perceive that thou art in the gall of bitterness, and in the bond of iniquity.

Romans 3:14
Whose mouth is full of cursing and bitterness:

Ephesians 4:31
Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:

Hebrews 12:15
Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled;