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]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "sept":
   affiliation, animal kingdom, apparentation, birth, blood,
   bloodline, bracket, branch, breed, brood, caste, category, clan,
   class, common ancestry, consanguinity, deme, derivation, descent,
   direct line, distaff side, division, estate, extraction, family,
   female line, filiation, folk, gens, grade, group, grouping, head,
   heading, house, kin, kind, label, level, line, line of descent,
   lineage, male line, matriclan, nation, order, patriclan, people,
   phratry, phyle, phylum, pigeonhole, plant kingdom, position,
   predicament, race, rank, rating, rubric, section, seed, set, side,
   spear side, species, spindle side, station, status, stem, stirps,
   stock, strain, stratum, subdivision, subgroup, suborder,
   succession, sword side, title, totem, tribe