The Collaborative International Dictionary of English v.0.48:

Concentrator \Con"cen*tra`tor\, n. (Mining)
   1. An apparatus for the separation of dry comminuted ore, by
      exposing it to intermittent puffs of air. --Knight.

   2. (Firearms) A frame or ring of wire or hard paper fitting
      into the cartridge case used in some shotguns, and holding
      the shot together when discharged, to secure close
      shooting; also, a device for slightly narrowing the bore
      at the muzzle for the same purpose.
      [Webster 1913 Suppl.] Concentric

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

concentrator

    A device that combines the data streams from
   many simultaneously active inputs into one shared channel in
   such a way that the streams can be separated after
   transmission.  The concentrator's output bandwidth must be at
   least as great as the total bandwidth of all simultaneously
   active inputs.  A concentrator is one kind of multiplexing
   device.

   For example, a concentrator may be used to connect 24 2400 bps
   TTYs to a host via a 57600 bps channel.

   (2000-03-01)