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