The Collaborative International Dictionary of English v.0.48:

Heighten \Height"en\ (h[imac]t"'n), v. t. [Written also
   highten.] [imp. & p. p. Heightened; p. pr. & vb. n.
   Heightening.]
   1. To make high; to raise higher; to elevate.
      [1913 Webster]

   2. To carry forward; to advance; to increase; to augment; to
      aggravate; to intensify; to render more conspicuous; --
      used of things, good or bad; as, to heighten beauty; to
      heighten a flavor or a tint. "To heighten our confusion."
      --Addison.
      [1913 Webster]

            An aspect of mystery which was easily heightened to
            the miraculous.                       --Hawthorne.
      [1913 Webster]

WordNet (r) 3.0 (2006):

heighten
    v 1: become more extreme; "The tension heightened" [syn:
         heighten, rise]
    2: make more extreme; raise in quantity, degree, or intensity;
       "heightened interest"
    3: increase; "This will enhance your enjoyment"; "heighten the
       tension" [syn: enhance, heighten, raise]
    4: increase the height of; "The athletes kept jumping over the
       steadily heightened bars"
    5: make (one's senses) more acute; "This drug will sharpen your
       vision" [syn: sharpen, heighten]
    6: make more intense, stronger, or more marked; "The efforts
       were intensified", "Her rudeness intensified his dislike for
       her"; "Pot smokers claim it heightens their awareness"; "This
       event only deepened my convictions" [syn: intensify,
       compound, heighten, deepen]