The Collaborative International Dictionary of English v.0.48:

Hiatus \Hi*a"tus\, n.; pl. L. Hiatus, E. Hiatuses. [L., fr.
   hiare, hiatum, to gape; akin to E. yawn. See Yawn.]
   1. An opening; an aperture; a gap; a chasm; esp., a defect in
      a manuscript, where some part is lost or effaced; a space
      where something is wanting; a break.
      [1913 Webster]

   2. (Gram.) The concurrence of two vowels in two successive
      words or syllables. --Pope.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hiatus
    n 1: an interruption in the intensity or amount of something
         [syn: suspension, respite, reprieve, hiatus,
         abatement]
    2: a missing piece (as a gap in a manuscript)
    3: a natural opening or perforation through a bone or a
       membranous structure [syn: foramen, hiatus]