The Collaborative International Dictionary of English v.0.48:

Septum \Sep"tum\, n.; pl. Septa. [L. septum, saeptum, an
   inclosure, hedge, fence, fr. sepire, saepire, to hedge in,
   inclose.]
   1. A wall separating two cavities; a partition; as, the nasal
      septum.
      [1913 Webster]

   2. (Bot.) A partition that separates the cells of a fruit.
      [1913 Webster]

   3. (Zool.)
      (a) One of the radial calcareous plates of a coral.
      (b) One of the transverse partitions dividing the shell of
          a mollusk, or of a rhizopod, into several chambers.
          See Illust. under Nautilus.
      (c) One of the transverse partitions dividing the body
          cavity of an annelid.
          [1913 Webster]

WordNet (r) 3.0 (2006):

septum
    n 1: (anatomy) a dividing partition between two tissues or
         cavities
    2: a partition or wall especially in an ovary

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "septum":
   barrier, brattice, buffer, buffer state, bulkhead, bumper, cloison,
   collision mat, cushion, diaphragm, dissepiment, dividing line,
   dividing wall, division, fender, interseptum, mat, midriff,
   midsection, pad, panel, paries, partition, party wall,
   property line, separation, septulum, shock pad, wall