Antonyms of adj harmless

1 sense of harmless

Sense 1
harmless (vs. harmful) -- (not causing or capable of causing harm; "harmless bacteria"; "rendered the bomb harmless")

harmful (vs. harmless) -- (causing or capable of causing harm; "too much sun is harmful to the skin"; "harmful effects of smoking")
        => abusive -- (characterized by physical or psychological maltreatment; "abusive punishment"; "argued...that foster homes are abusive")
        => bad -- (capable of harming; "bad air"; "smoking is bad for you")
        => bruising -- (causing mental or emotional injury; "a bruising experience"; "protected from the bruising facts of battle"- John Mason Brown)
        => deleterious, hurtful, injurious -- (harmful to living things; "deleterious chemical additives")
        => calumniatory, calumnious, defamatory, denigrative, denigrating, denigratory, libellous, libelous, slanderous -- ((used of statements) harmful and often untrue; tending to discredit or malign)
        => catastrophic, ruinous -- (extremely harmful; bringing physical or financial ruin; "a catastrophic depression"; "catastrophic illness"; "a ruinous course of action")
        => counterproductive -- (tending to hinder the achievement of a goal)
        => damaging, detrimental, prejudicial, prejudicious -- ((sometimes followed by `to') causing harm or injury; "damaging to career and reputation"; "the reporter's coverage resulted in prejudicial publicity for the defendant")
        => ill -- (resulting in suffering or adversity; "ill effects"; "it's an ill wind that blows no good")
        => insidious, pernicious, subtle -- (working or spreading in a hidden and usually injurious way; "glaucoma is an insidious disease"; "a subtle poison")
        => mischievous -- (deliberately causing harm or damage; "mischievous rumors and falsehoods")
        => nocent -- (having a tendency to cause harm)
        => stabbing, wounding -- (causing physical or especially psychological injury; "a stabbing remark"; "wounding and false charges of disloyalty")

Similarity of adj harmless

1 sense of harmless

Sense 1
harmless (vs. harmful) -- (not causing or capable of causing harm; "harmless bacteria"; "rendered the bomb harmless")
       => innocent, innocuous -- (lacking intent or capacity to injure; "an innocent prank")
          Also See-> benign#2, benignant#1; innocuous#1; nontoxic#1, atoxic#1; painless#2; safe#1