Source : Webster's Revised Unabridged Dictionary (1913)

Harmful \Harm"ful\, a.
   Full of harm; injurious; hurtful; mischievous. `` Most
   harmful hazards.'' --Strype. --{Harm"ful*ly}, adv. --
   {Harm"ful*ness}, n.

Source : WordNet®

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}]