The Collaborative International Dictionary of English v.0.48:

Apparatus \Ap"pa*ratus\, n.; pl. Apparatus, also rarely
   Apparatuses. [L., from apparare, apparatum, to prepare; ad
   + prepare to make ready.]
   1. Things provided as means to some end.
      [1913 Webster]

   2. Hence: A full collection or set of implements, or
      utensils, for a given duty, experimental or operative; any
      complex instrument or appliance, mechanical or chemical,
      for a specific action or operation; machinery; mechanism.
      [1913 Webster]

   3. (Physiol.) A collection of organs all of which unite in a
      common function; as, the respiratory apparatus.
      [1913 Webster]

WordNet (r) 3.0 (2006):

apparatus
    n 1: equipment designed to serve a specific function [syn:
         apparatus, setup]
    2: (anatomy) a group of body parts that work together to perform
       a given function; "the breathing apparatus"