early 14c. (implied in viciously), "of the nature of vice, wicked," from Anglo-Fr. vicious, O.Fr. vicieus, from L. vitiosus "faulty, defective, corrupt," from vitium "fault" (see vice
(1)). Meaning "inclined to be savage or dangerous" is first recorded 1711 (originally of animals,
especially horses); that of "full of spite, bitter, severe" is from 1825. In law, "marred by some inherent fault" (late 14c.), hence also this sense in logic (c.1600); cf. vicious circle in reasoning (c.1792), which was given a general sense of "a situation in which action and reaction intensify one another" by 1839.