Source : Webster's Revised Unabridged Dictionary (1913)

Harm \Harm\, v. t. [imp. & p. p. {Harmed}; p. pr. & vb. n.
   {Harming}.] [OE. harmen, AS. hearmian. See {Harm}, n.]
   To hurt; to injure; to damage; to wrong.

         Though yet he never harmed me.           --Shak.

         No ground of enmity between us known Why he should mean
         me ill or seek to harm.                  --Milton.

Harm \Harm\, n. [OE. harm, hearm, AS. hearm; akin to OS. harm,
   G. harm grief, Icel. harmr, Dan. harme, Sw. harm; cf. OSlav.
   & Russ. sram' shame, Skr. crama toil, fatigue.]
   1. Injury; hurt; damage; detriment; misfortune.

   2. That which causes injury, damage, or loss.

            We, ignorant of ourselves, Beg often our own harms.
                                                  --Shak.

   Syn: Mischief; evil; loss; injury. See {Mischief}.

Source : WordNet®

harm
     n 1: any physical damage to the body caused by violence or
          accident or fracture etc. [syn: {injury}, {hurt}, {trauma}]
     2: the occurrence of a change for the worse [syn: {damage}, {impairment}]
     3: the act of damaging something or someone [syn: {damage}, {hurt},
         {scathe}]

harm
     v : cause or do harm to; "These pills won't harm your system"