The Collaborative International Dictionary of English v.0.48:

Baneful \Bane"ful\, a.
   Having poisonous qualities; deadly; destructive; injurious;
   noxious; pernicious. "Baneful hemlock." --Garth. "Baneful
   wrath." --Chapman.
   [1913 Webster] -- Bane"ful*ly, adv. --Bane"ful*ness, n.
   [1913 Webster]