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