The Collaborative International Dictionary of English v.0.48:

Houri \Hou"ri\, n.; pl. Houris. [Per. h[=u]r[imac],
   h[=u]r[=a], h[=u]r; akin to Ar. h[=u]r, pl. of ahwar
   beautiful-eyed, black-eyed.]
   A nymph of paradise; -- so called by the Mohammedans.
   [1913 Webster]

WordNet (r) 3.0 (2006):

houri
    n 1: a voluptuously beautiful young woman [syn: nymph,
         houri]
    2: (Islam) one of the dark-eyed virgins of perfect beauty
       believed to live with the blessed in Paradise

The Devil's Dictionary (1881-1906):

HOURI, n.  A comely female inhabiting the Mohammedan Paradise to make
things cheery for the good Mussulman, whose belief in her existence
marks a noble discontent with his earthly spouse, whom he denies a
soul.  By that good lady the Houris are said to be held in deficient
esteem.