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]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "hiatus":
   aperture, arrearage, breach, break, broaching, caesura, cavity,
   cessation, chasm, check, clearance, clearing, cleft, crack,
   defalcation, defect, deficiency, deficit, disclosure,
   discontinuity, distance between, double space, em space, en space,
   fenestra, fissure, fistula, fontanel, foramen, freeboard, gap,
   gape, gat, gulf, hair space, half space, hole, hollow, inlet,
   interim, intermediate space, intermission, interruption,
   interspace, interstice, interval, jump, lack, lacuna, laying open,
   leak, leap, leeway, letup, lull, margin, missing link, need,
   omission, opening, opening up, orifice, outage, outlet, passageway,
   pause, pore, room, shortage, single space, slot, space,
   space between, split, stoma, suspension, throwing open,
   time interval, ullage, uncorking, unstopping, want, wantage,
   yawn