The Collaborative International Dictionary of English v.0.48:

Armature \Ar"ma*ture\, n. [L. armatura, fr. armare to arm: cf.
   F. armature. See Arm, v. t., Armor.]
   1. Armor; whatever is worn or used for the protection and
      defense of the body, esp. the protective outfit of some
      animals and plants.
      [1913 Webster]

   2. (Magnetism) A piece of soft iron used to connect the two
      poles of a magnet, or electro-magnet, in order to complete
      the circuit, or to receive and apply the magnetic force.
      In the ordinary horseshoe magnet, it serves to prevent the
      dissipation of the magnetic force.
      [1913 Webster]

   3. (Arch.) Iron bars or framing employed for the
      consolidation of a building, as in sustaining slender
      columns, holding up canopies, etc. --Oxf. Gloss.
      [1913 Webster]

   4. (Elec.) That moving part of a dynamo or electric generator
      in which a current is induced by a moving through a
      magnetic field, or, in an electric motor, the part through
      which the applied current moves, thereby generating
      torque. The armature usually consists of a series of coils
      or groups of insulated conductors surrounding a core of
      iron.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

armature
    n 1: coil in which voltage is induced by motion through a
         magnetic field