The Collaborative International Dictionary of English v.0.48:

feedback \feedback\ n.
   1. the process in which part of the output of a system is
      returned to its input.
      [WordNet 1.5]

   2. response to an inquiry or experiment.
      [WordNet 1.5] feedbag

WordNet (r) 3.0 (2006):

feedback
    n 1: the process in which part of the output of a system is
         returned to its input in order to regulate its further
         output
    2: response to an inquiry or experiment

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "feedback":
   birdies, blooping, blurping, closed loop, closed sequence,
   current-control circuit, degeneration, distortion,
   flip-flop circuit, flutter, fluttering, hissing, howling, hum,
   motorboating, positive feedback, process loop, quality loop,
   reversed feedback, rumble, scratching, shredding, squeals, static,
   whistles, woomping, wow, wowwows



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

feedback

    Part of a system output presented at its input.
   Feedback may be unintended.  When used as a design feature,
   the output is usually transformed by passive components which
   attenuate it in some manner; the result is then presented at
   the system input.

   Feedback is positive or negative, depending on the sign with
   which a positive change in the original input reappears after
   transformation.  Negative feedback was invented by Black to
   stabilise vacuum tube amplifiers.  The behaviour becomes
   largely a function of the feedback transformation and only
   minimally a function of factors such as transistor gain which
   are imperfectly known.

   Positive feedback can lead to instability; it finds wide
   application in the construction of oscillators.

   Feedback can be used to control a system, as in feedback
   control.

   (1996-01-02)