Synonyms for Baneful:

adj.

all (adjective)
deadly, pernicious, pestilent.
bad (adjective)
displeasing, arrant, vile, unfavorable, unsatisfactory, bad, unsound, detrimental, inadvisable, ill-suited, poor, wretched, irremediable, wrong, defective, faulty, inadequate, inferior, unpleasant, black, invalid.
baneful (adjective)
contagious, infectious, calamitous, evil, ill, poisonous, cancerous, cursed.
dangerous (adjective)
pestilent.
evil (adjective)
satanic, detrimental, evil, bad, depraved, revolting, heinous, disgraceful, reprehensible, repellent, repulsive, sinful, calamitous, nefarious, hideous, wicked, sinister, loathsome, atrocious, maleficent, repugnant, damnable, destructive, diabolical, villainous, foul, terrible, Fiendish, offensive, monstrous, abominable, devilish.
fateful (adjective)
hellfire.
harmful (adjective)
poisonous.
malevolent (adjective)
churlish, Black-hearted, evil, malevolent, baleful, hateful, sullen, corrosive, treacherous, foul, malicious, mean, rancorous, perfidious, antagonistic, malignant, sinister, wicked, spiteful, virulent, nasty, bitter, venomous, vindictive, ill-natured, hurtful, catty, hostile, vicious.
ruinous, injurious (adjective)
noxious, pestilent, harmful, baleful, hurtful, poisonous, pernicious, wicked, destructive, evil, calamitous, venomous, deadly.

n.

help. dire, fire and brimstone, direful, hellfire, luck, portentous, warn, apocalyptical, unlucky, grave, fateful, apocalyptic. baneful (noun)
deadly, baleful, harmful, noxious, pernicious, pestilent, maleficent.

Other synonyms:

fire and brimstone, apocalyptical, hellfire, apocalyptic. direful, dire. unlucky, portentous. fateful. Other relevant words:
maleficent, apocalyptical, hellfire, help, noxious, warn, dire, satanic, fateful, depraved, pernicious, unlucky, direful, villainous, devilish, diabolical, grave, harmful, deadly, pestilent, portentous, luck, apocalyptic, Fiendish.