The Collaborative International Dictionary of English v.0.48:

Sept \Sept\, n. [A corruption of sect, n.]
   A clan, tribe, or family, proceeding from a common
   progenitor; -- used especially of the ancient clans in
   Ireland.
   [1913 Webster]

         The chief, struck by the illustration, asked at once to
         be baptized, and all his sept followed his example.
                                                  --S. Lover.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Sept
    n 1: the month following August and preceding October [syn:
         September, Sep, Sept]
    2: people descended from a common ancestor; "his family has
       lived in Massachusetts since the Mayflower" [syn: family,
       family line, folk, kinfolk, kinsfolk, sept,
       phratry]