• (a.) Having the orbital index relatively large; having the orbits narrow transversely; -- opposed to microseme.
Meg'a·seme adjective [ Mega- + Greek ... sing, mark: confer French mégasème .] (Anat.) Having the orbital index relatively large; having the orbits narrow transversely; -- opposed to microseme . 
Type: Term Pronunciation: meg′ă-sēm Definitions: 1. Denoting an orbital aperture with an index above 89.