Synonyms for Baneful (same or very similar meaning)
WordNet sense 1 (exceedingly harmful):
deadly, pernicious, pestilentWordNet sense 2 (injurious to physical or mental health):
harmful, noxiousWordNet sense 3 (deadly or sinister):
balefulWordNet sense 4 (harmful or evil in intent or effect):
maleficent, maleficentFrom the ODE community, based on WordNetadd/edit