Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

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

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.

   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.

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

Source : WordNet®

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