The Collaborative International Dictionary of English v.0.48:

Imagery \Im"age*ry\ ([i^]m"[asl]j*r[y^]; 277), n. [OE. imagerie,
   F. imagerie.]
   1. The work of one who makes images or visible representation
      of objects; imitation work; images in general, or in mass.
      "Painted imagery." --Shak.
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            In those oratories might you see
            Rich carvings, portraitures, and imagery. --Dryden.
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   2. Fig.: Unreal show; imitation; appearance.
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            What can thy imagery of sorrow mean?  --Prior.
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   3. The work of the imagination or fancy; false ideas;
      imaginary phantasms.
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            The imagery of a melancholic fancy.   --Atterbury.
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   4. Rhetorical decoration in writing or speaking; vivid
      descriptions presenting or suggesting images of sensible
      objects; figures in discourse.
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            I wish there may be in this poem any instance of
            good imagery.                         --Dryden.
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WordNet (r) 3.0 (2006):

imagery
    n 1: the ability to form mental images of things or events; "he
         could still hear her in his imagination" [syn:
         imagination, imaging, imagery, mental imagery]