The Collaborative International Dictionary of English v.0.48:

Plumber \Plumb"er\, n. [F. plombier. See Plumb.]
   One who works in lead; esp., one who furnishes, fits, and
   repairs lead pipes.
   [1913 Webster]

   2. Hence: Any worker who installs or repairs piping and
      related equipment for conveyance of water, gas, or
      drainage into or out of buildings, or within buildings to
      fixtures or equipment using water. The type of material
      used for the conduits varies with the application, and may
      be may be of lead, iron, copper, glass, palstic, or other
      material.
      [PJC]

WordNet (r) 3.0 (2006):

plumber
    n 1: a craftsman who installs and repairs pipes and fixtures and
         appliances [syn: plumber, pipe fitter]

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

Plumber

    A system for obtaining information about
   memory leaks in Ada and C programs.

   (http://home.earthlink.net/~owenomalley/plumber.html).

   (17 Feb 1999)