From WordNet (r) 2.0 (August 2003) [wn]:
harmful
adj 1: injurious to physical or mental health; "noxious chemical
wastes"; "noxious ideas" [syn: noxious] [ant:
innocuous]
2: able or likely to do harm
3: causing or capable of causing harm; "too much sun is harmful
to the skin"; "harmful effects of smoking" [ant:
harmless]
4: constituting a disadvantage [syn: disadvantageous] [ant:
advantageous]
5: contrary to your interests or welfare; "adverse
circumstances"; "made a place for themselves under the
most untoward conditions" [syn: adverse, inauspicious,
untoward]
6: tending to cause great harm [syn: evil, injurious]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Harmful \Harm"ful\ (h[aum]rm"f[.u]l), a.
Full of harm; injurious; hurtful; mischievous. " Most harmful
hazards." --Strype. --Harm"ful*ly, adv. -- Harm"ful*ness,
n.
[1913 Webster]