Definition (Adjective) Of a thing, action, intent, etc.: causing or likely to cause harm, especially in a gradual or insidious manner; dangerous, destructive; evil. Also in weakened use: having a harmful influence; undesirable. In Context "His mother was affectionate, but also exacting and somewhat censorious; she was firmly persuaded that only the pernicious influence of ill-chosen friends had seduced her son from the evangelical principles which she had inculcated in his youth." Edward Tyas Cook, The Life of John Ruskin: Volume 2, 1860-1900, 1911.