Source : Webster's Revised Unabridged Dictionary (1913)

Impression \Im*pres"sion\, n. [F. impression, L. impressio.]
   1. The act of impressing, or the state of being impressed;
      the communication of a stamp, mold, style, or character,
      by external force or by influence.

   2. That which is impressed; stamp; mark; indentation;
      sensible result of an influence exerted from without.

            The stamp and clear impression of good sense.
                                                  --Cowper.

            To shelter us from impressions of weather, we must
            spin, we must weave, we must build.   --Barrow.

   3. That which impresses, or exercises an effect, action, or
      agency; appearance; phenomenon. [Obs.]

            Portentous blaze of comets and impressions in the
            air.                                  --Milton.

            A fiery impression falling from out of Heaven.
                                                  --Holland.

   4. Influence or effect on the senses or the intellect hence,
      interest, concern. --Reid.

            His words impression left.            --Milton.

            Such terrible impression made the dream. --Shak.

            I have a father's dear impression, And wish, before
            I fall into my grave, That I might see her married.
                                                  --Ford.

   5. An indistinct notion, remembrance, or belief.

   6. Impressiveness; emphasis of delivery.

            Which must be read with an impression. --Milton.

   7. (Print.) The pressure of the type on the paper, or the
      result of such pressure, as regards its appearance; as, a
      heavy impression; a clear, or a poor, impression; also, a
      single copy as the result of printing, or the whole
      edition printed at a given time.

            Ten impressions which his books have had. --Dryden.

   8. In painting, the first coat of color, as the priming in
      house painting and the like. [R.]

   9. (Engraving) A print on paper from a wood block, metal
      plate, or the like.

   {Proof impression}, one of the early impressions taken from
      an engraving, before the plate or block is worn.

Source : WordNet®

impression
     n 1: a vague idea in which some confidence is placed; "his
          impression of her was favorable"; "what are your
          feelings about the crisis?"; "it strengthened my belief
          in his sincerity"; "I had a feeling that she was lying"
          [syn: {feeling}, {belief}, {notion}, {opinion}]
     2: an outward appearance; "he made a good impression"; "I
        wanted to create an impression of success"; "she retained
        that bold effect in her reproductions of the original
        painting" [syn: {effect}]
     3: a clear and telling mental image; "he described his mental
        picture of his assailant"; "he had no clear picture of
        himself or his world"; "the events left a permanent
        impression in his mind" [syn: {mental picture}, {picture}]
     4: a concavity in a surface produced by pressing; "he left the
        impression of his fingers in the soft mud" [syn: {depression},
         {imprint}]
     5: a symbol that is the result of printing; "he put his stamp
        on the envelope" [syn: {stamp}]
     6: all the copies of a work printed at one time; "they ran off
        an initial printing of 2000 copies" [syn: {printing}]
     7: (dentistry) an imprint of the teeth and gums in wax or
        plaster; "the dentist took an impression for use in
        preparing an inlay"
     8: an impressionistic portrayal of a person; "he did a funny
        impression of a politician"
     9: the act of pressing one thing on or into the surface of
        another; "he watched the impression of the seal on the hot
        wax"