Middle English balefull "(of humans or animals) bent upon mischief or destruction, malevolent, (of things) pernicious," also "wretched, miserable," going back to Old English bealluful "full of evil, sinful," from bealu + -ful
adjective
deadly or pernicious in influence
foreboding or threatening evil
baleful effects
sinisterbalefulmalign mean seriously threatening evil or disaster. sinister suggests a general or vague feeling of fear or apprehension on the part of the observer. baleful imputes perniciousness or destructiveness to something whether working openly or covertly.