Source : Webster's Revised Unabridged Dictionary (1913)

Unloosen \Un*loos"en\, v. t. [1st pref. un- (intensive) +
   loosen.]
   To loosen; to unloose.

Source : WordNet®

unloosen
     v 1: grant freedom to; free from confinement [syn: {free}, {liberate},
           {release}, {unloose}, {loose}] [ant: {confine}]
     2: loosen the ties of; "unloose your sneakers" [syn: {unloose}]