Source : Webster's Revised Unabridged Dictionary (1913)

Loosen \Loos"en\, v. i.
   To become loose; to become less tight, firm, or compact. --S.
   Sharp.

Loosen \Loos"en\, v. t. [imp. & p. p. {Loosened}; p. pr. & vb.
   n. {Loosening}.] [See {Loose}, v. t.]
   1. To make loose; to free from tightness, tension, firmness,
      or fixedness; to make less dense or compact; as, to loosen
      a string, or a knot; to loosen a rock in the earth.

            After a year's rooting, then shaking doth the tree
            good by loosening of the earth.       --Bacon.

   2. To free from restraint; to set at liberty..

            It loosens his hands, and assists his understanding.
                                                  --Dryden.

   3. To remove costiveness from; to facilitate or increase the
      alvine discharges of. --Bacon.

Source : WordNet®

loosen
     v 1: make loose or looser; "loosen the tension on a rope" [syn: {loose}]
          [ant: {stiffen}]
     2: make less severe or strict; "The government relaxed the
        curfew after most of the rebels were caught" [syn: {relax}]
     3: become less severe or strict; "The rules relaxed after the
        new director arrived" [syn: {relax}]
     4: disentangle and raise the fibers of; "tease wool" [syn: {tease},
         {tease apart}]
     5: cause to become loose; "undo the shoelace"; "untie the
        knot"; "loosen the necktie" [syn: {untie}, {undo}]
     6: make less dense; "loosen the soil"
     7: become loose or looser or less tight; "The noose loosened";
        "the rope relaxed" [syn: {relax}, {loose}] [ant: {stiffen}]