Source : Webster's Revised Unabridged Dictionary (1913)

Unleash \Un*leash"\, v. t. [1st pref. un- + leash.]
   To free from a leash, or as from a leash; to let go; to
   release; as, to unleash dogs.

Source : WordNet®

unleash
     v 1: release or vent; "unleash one's anger"
     2: release from a leash; "unleash the dogs in the park"
     3: turn loose or free from restraint; "let loose mines"; "Loose
        terrible plagues upon humanity" [syn: {let loose}, {loose}]