Vicious, a. — Webster enters it under “vicious”
Etymology: [OF. vicious, F. vicieux, fr. L. vitiosus, fr. vitium vice. See Vice a fault.]
1. Characterized by vice or defects; defective; faulty; imperfect. Though I perchance am vicious in my guess. Shak. The title of these lords was vicious in its origin. Burke. A charge against Bentley of vicious reasoning. De Quincey.
2. Addicted to vice; corrupt in principles or conduct; depraved; wicked; as, vicious children; vicious examples; vicious conduct. Who . . . heard this heavy curse, Servant of servants, on his vicious race. Milton.
3. Wanting purity; foul; bad; noxious; as, vicious air, water, etc. Dryden.
4. Not correct or pure; corrupt; as, vicious language; vicious idioms.
3 more senses
5. Not well tamed or broken; given to bad tricks; unruly; refractory; as, a vicious horse.
6. Bitter; spiteful; malignant. [Colloq.]
Syn. -- Corrupt; faulty; wicked; depraved. -- Vi"cious*ly, adv. -- Vi"cious*ness, n.
Shades of meaning
Fernald has no entry of its own for viciousness; he lists it under sin.
He lists it without comment; the entries above explain its neighbors.