Looks like a glaive socket, European, maybe 16th, 17th century. Parade/guard/processional glaive, rather than a battlefield weapon. Looks like it might have had langets.
Some complete examples, with similar sockets and "guard" at socket/blade junction:
http://www.clevelandart.org/art/1916.1536
http://www.clevelandart.org/art/1916.1532
http://www.metmuseum.org/collection/...e/search/25093
http://www.metmuseum.org/collection/...e/search/21953
http://www.metmuseum.org/collection/...e/search/25016
http://www.metmuseum.org/collection/...e/search/26794
(but most of these have short "wings" at the base of the blade)