foramen

from WordNet (r) 3.0 (2006)

foramen
    n 1: a natural opening or perforation through a bone or a
         membranous structure [syn: {foramen}, {hiatus}]

from The Collaborative International Dictionary of English v.0.48

Foramen \Fo*ra"men\, n.; pl. L. {Foramina}, E. {Foramines}. [L.,
   fr. forare to bore, pierce.]
   A small opening, perforation, or orifice; a fenestra.
   [1913 Webster]

   {Foramen of Monro} (Anat.), the opening from each lateral
      into the third ventricle of the brain.

   {Foramen of Winslow} (Anat.), the opening connecting the sac
      of the omentum with the general cavity of the peritoneum.
      [1913 Webster]