Bitter, Bitterly, Bitterness - Vine's Expository Dictionary of New Testament Words
Bitter, Bitterly, Bitterness[ A-1,Adjective,G4089, pikros ]
from a root pik, meaning to cut, to prick," hence, lit., "pointed, sharp, keen, pungent to the sense of taste, smell, etc.," is found in James 3:11, James 3:14. In James 3:11 it has its natural sense, with reference to water; in James 3:14 it is used metaphorically of jealousy, RV.
[ B-1,Verb,G4087, pikraino ]
related to A, signifies, in the Active Voice, "to be bitter," Colossians 3:19, or "to embitter, irritate, or to make bitter," Revelation 10:9; the Passive Voice, "to be made bitter," is used in Revelation 8:11; Revelation 10:10.
[ C-1,Noun,G4088, pikria ]
denotes "bitterness." It is used in Acts 8:23, metaphorically, of a condition of extreme wickedness, "gall of bitterness" or "bitter gal;" in Romans 3:14, of evil speaking; in Ephesians 4:31, of "bitter" hatred; in Hebrews 12:15, in the same sense, metaphorically, of a root of "bitterness," producing "bitter" fruit.
[ D-1,Adverb,G4090, pikros ]
"bitterly," is used of the poignant grief of Peter's weeping for his denial of Christ, Matthew 26:75; Luke 22:62.
Note: In the Sept., pikros (not in the NT), "a bitter herb," is used in Exodus 12:8; Numbers 9:11.