From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
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"