The Collaborative International Dictionary of English v.0.48:

Intensify \In*ten"si*fy\, v. i.
   To become intense, or more intense; to act with increasing
   power or energy.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intensify \In*ten"si*fy\, v. t. [imp. & p. p. Intensified; p.
   pr. & vb. n. Intensifying.] [Intense + -fly.]
   To render more intense; as, to intensify heat or cold; to
   intensify colors; to intensify a photographic negative; to
   intensify animosity. --Bacon.
   [1913 Webster]

         How piercing is the sting of pride
         By want embittered and intensified.      --Longfellow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intensify
    v 1: increase in extent or intensity; "The Allies escalated the
         bombing" [syn: escalate, intensify, step up] [ant:
         de-escalate, step down, weaken]
    2: make more intense, stronger, or more marked; "The efforts
       were intensified", "Her rudeness intensified his dislike for
       her"; "Pot smokers claim it heightens their awareness"; "This
       event only deepened my convictions" [syn: intensify,
       compound, heighten, deepen]
    3: become more intense; "The debate intensified"; "His dislike
       for raw fish only deepened in Japan" [syn: intensify,
       deepen]
    4: make the chemically affected part of (a negative) denser or
       more opaque in order produce a stronger contrast between
       light and dark