From 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]