NOUN (2)

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;

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

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