Source : Webster's Revised Unabridged Dictionary (1913)

Intensity \In*ten"si*ty\, n. [LL. intensitas: cf. F.
   intensit['e]. See {Intense}.]
   1. The state or quality of being intense; intenseness;
      extreme degree; as, intensity of heat, cold, mental
      application, passion, etc.

            If you would deepen the intensity of light, you must
            be content to bring into deeper blackness and more
            distinct and definite outline the shade that
            accompanies it. --F. W. Robertson.

   2. (Physics) The amount or degree of energy with which a
      force operates or a cause acts; effectiveness, as
      estimated by results produced.

   3. (Mech.) The magnitude of a distributed force, as pressure,
      stress, weight, etc., per unit of surface, or of volume,
      as the case may be; as, the measure of the intensity of a
      total stress of forty pounds which is distributed
      uniformly over a surface of four square inches area is ten
      pounds per square inch.

   4. (Photog.) The degree or depth of shade in a picture.

Source : WordNet®

intensity
     n 1: the amount of energy transmitted (as by acoustic or
          electromagnetic radiation); "he adjusted the intensity
          of the sound"; "they measured the station's signal
          strength" [syn: {strength}, {intensity level}]
     2: high level or degree; the property of being intense [syn: {intensiveness}]
     3: the magnitude of sound (usually in a specified direction);
        "the kids played their music at full volume" [syn: {volume},
         {loudness}] [ant: {softness}]
     4: chromatic purity: freedom from dilution with white and hence
        vividness of hue [syn: {saturation}, {chroma}, {vividness}]