Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

            An aspect of mystery which was easily heightened to
            the miraculous.                       --Hawthorne.

Source : WordNet®

heightening
     adj : reaching a higher intensity; "their heightening fears" [syn:
            {heightening(a)}]