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