The Collaborative International Dictionary of English v.0.48:

Orifice \Or"i*fice\, n. [F., from L. orificium; os, oris, a
   mouth + facere to make. See Oral, and Fact.]
   A mouth or aperture, as of a tube, pipe, etc.; an opening;
   as, the orifice of an artery or vein; the orifice of a wound.
   --Shak.
   [1913 Webster]

         Etna was bored through the top with a monstrous
         orifice.                                 --Addison.
   [1913 Webster] Oriflamb

WordNet (r) 3.0 (2006):

orifice
    n 1: an aperture or hole that opens into a bodily cavity; "the
         orifice into the aorta from the lower left chamber of the
         heart" [syn: orifice, opening, porta]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "orifice":
   aperture, broaching, cavity, chasm, check, clearing, cleft, crack,
   disclosure, fenestra, fistula, fontanel, foramen, gap, gape, gat,
   gulf, hiatus, hole, hollow, inlet, interval, lacuna, laying open,
   leak, opening, opening up, outlet, passageway, pore, slot, space,
   split, stoma, throwing open, uncorking, unstopping, vent, yawn