The Collaborative International Dictionary of English v.0.48:

Plumbing \Plumb"ing\, n.
   1. The art of casting and working in lead, and applying it to
      building purposes; especially, the business of furnishing,
      fitting, and repairing pipes for conducting water, sewage,
      etc. --Gwilt.
      [1913 Webster]

   2. The lead or iron pipes, and other apparatus, used in
      conveying water, sewage, etc., in a building.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plumb \Plumb\, v. t. [imp. & p. p. Plumbed (pl[u^]md); p. pr.
   & vb. n. Plumbing (pl[u^]m"[i^]ng).]
   1. To adjust by a plumb line; to cause to be perpendicular;
      as, to plumb a building or a wall.
      [1913 Webster]

   2. To sound with a plumb or plummet, as the depth of water;
      hence, to examine by test; to ascertain the depth,
      quality, dimension, etc.; to sound; to fathom; to test.
      [1913 Webster]

            He did not attempt to plumb his intellect. --Ld.
                                                  Lytton.
      [1913 Webster]

   3. To seal with lead; as, to plumb a drainpipe.
      [1913 Webster]

   4. To supply, as a building, with a system of plumbing.
      [1913 Webster]

WordNet (r) 3.0 (2006):

plumbing
    n 1: utility consisting of the pipes and fixtures for the
         distribution of water or gas in a building and for the
         disposal of sewage [syn: plumbing, plumbing system]
    2: the occupation of a plumber (installing and repairing pipes
       and fixtures for water or gas or sewage in a building) [syn:
       plumbing, plumbery]
    3: measuring the depths of the oceans [syn: bathymetry,
       plumbing]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "plumbing":
   accouterments, apparatus, appliances, appointments, appurtenances,
   armament, conveniences, duffel, equipage, equipment, facilities,
   facility, fittings, fixtures, furnishings, furniture, gear,
   impedimenta, installations, kit, machinery, materiel, munition,
   munitions, outfit, paraphernalia, plant, rig, rigging,
   stock-in-trade, tackle, things, utensils



The Jargon File (version 4.4.7, 29 Dec 2003):

plumbing
 n.

    [Unix] Term used for shell code, so called because of the prevalence of
    pipelines that feed the output of one program to the input of another.
    Under Unix, user utilities can often be implemented or at least prototyped
    by a suitable collection of pipelines and temp-file grinding encapsulated
    in a shell script; this is much less effort than writing C every time, and
    the capability is considered one of Unix's major winning features. A few
    other OSs such as IBM's VM/CMS support similar facilities. Esp.: used in
    the construction hairy plumbing (see hairy). ?You can kluge together a
    basic spell-checker out of sort(1), comm(1), and tr(1) with a little
    plumbing.? See also tee.


The Free On-line Dictionary of Computing (30 December 2018):

plumbing

   (Unix) Term used for shell code, so called because of the
   prevalence of "pipelines" that feed the output of one
   program to the input of another.  Under Unix, user utilities
   can often be implemented or at least prototyped by a suitable
   collection of pipelines and temporary file grinding
   encapsulated in a shell script.  This is much less effort
   than writing C every time, and the capability is considered
   one of Unix's major winning features.  A few other operating
   systems such as IBM's VM/CMS support similar facilities.

   The tee utility is specifically designed for plumbing.

   [Jargon File]

   (1995-02-23)