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]

WordNet (r) 3.0 (2006):

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