The Collaborative International Dictionary of English v.0.48:

Endogamy \En*dog"a*my\, n.
   Marriage only within the tribe; a custom restricting a man in
   his choice of a wife to the tribe to which he belongs; --
   opposed to exogamy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

endogamy
    n 1: marriage within one's own tribe or group as required by
         custom or law [syn: endogamy, intermarriage,
         inmarriage] [ant: exogamy, intermarriage]