Source : Webster's Revised Unabridged Dictionary (1913)

Lynch \Lynch\, v. t. [imp. & p. p. {Lynched}; p. pr. & vb. n.
   {Lynching}.] [See Note under {Lynch law}.]
   To inflict punishment upon, especially death, without the
   forms of law, as when a mob captures and hangs a suspected
   person. See {Lynch law}.

Source : WordNet®

lynch
     v : kill without legal sanction; "The blood-thirsty mob lynched
         the alleged killer of the child"