Source : Webster's Revised Unabridged Dictionary (1913)

Half tone \Half tone\, or Half-tone \Half"-tone`\, n.
   1. (Fine Arts)
      (a) An intermediate or middle tone in a painting,
          engraving, photograph, etc.; a middle tint, neither
          very dark nor very light.
      (b) A half-tone photo-engraving.

   2. (Music) A half step.

Half-tone \Half"-tone`\, a.
   Having, consisting of, or pertaining to, half tones; specif.
   (Photo-engraving), pertaining to or designating plates,
   processes, or the pictures made by them, in which gradation
   of tone in the photograph is reproduced by a graduated system
   of dotted and checkered spots, usually nearly invisible to
   the unaided eye, produced by the interposition between the
   camera and the object of a screen. The name alludes to the
   fact that this process was the first that was practically
   successful in reproducing the half tones of the photograph.