“mischievous”— Webster’s definition

Mis"chie*vous (?), a. Causing mischief; harmful; hurtful; -- now often applied where the evil is done carelessly or in sport; as, a mischievous child. Most mischievous foul sin." Shak.

This false, wily, doubling disposition is intolerably mischievous to society. South.

Synonyms -- Harmful; hurtful; detrimental; noxious; pernicious; destructive.