Bitterness, n.
Etymology: [AS. biternys; biter better + -nys = -ness.]
1. The quality or state of being bitter, sharp, or acrid, in either a literal or figurative sense; implacableness; resentfulness; severity; keenness of reproach or sarcasm; deep distress, grief, or vexation of mind. The lip that curls with bitterness. Percival. I will complain in the bitterness of my soul. Job vii. 11.
2. A state of extreme impiety or enmity to God. Thou art in the gall of bitterness, and in the bond of iniquity. Acts viii. 23.
3. Dangerous error, or schism, tending to draw persons to apostasy. Looking diligently, . . . lest any root of bitterness springing up trouble you. Heb. xii. 15.
Shades of meaning
Fernald has no entry of its own for bitterness; he lists it under acrimony, enmity, feud.
Where he writes about it:
Acerbity is a sharpness, with a touch of bitterness, which may arise from momentary annoyance or habitual impatience; asperity is keener and more pronounced, denoting distinct irritation or vexation; in speech asperity is often manifested by the tone of voice rather than by the words that are spoken. — from acrimony
Bitterness is a resentful feeling arising from a belief that one has been wronged; acrimony is a kindred feeling, but deeper and more persistent, and may arise from the crossing of one's wishes or plans by another, where no injustice or wrong is felt. — from enmity
Bitterness is in feeling only; enmity and hostility involve will and purpose to oppose or injure. — from feud