The Collaborative International Dictionary
Veneficial
Veneficial \Ven`e*fi"cial\, Veneficious \Ven`e*fi"cious\, a.
Acting by poison; used in poisoning or in sorcery. [Obs.]
``An old veneficious practice.''
--Sir T. Browne. --
Ven`e*fi"cious*ly, adv. [Obs.]
Wiktionary
veneficial
a. (context dated now rare English) poisonous or poisoning; pertaining to poison; malignant, sorcerous.