Source : Webster's Revised Unabridged Dictionary (1913)

Deepen \Deep"en\, v. t. [imp. & p. p. {Deepened}; p. pr. & vb.
   n. {Deepening}.]
   1. To make deep or deeper; to increase the depth of; to sink
      lower; as, to deepen a well or a channel.

            It would . . . deepen the bed of the Tiber.
                                                  --Addison.

   2. To make darker or more intense; to darken; as, the event
      deepened the prevailing gloom.

            You must deepen your colors.          --Peacham.

   3. To make more poignant or affecting; to increase in degree;
      as, to deepen grief or sorrow.

   4. To make more grave or low in tone; as, to deepen the tones
      of an organ.

            Deepens the murmur of the falling floods. --Pope.

Source : WordNet®

deepening
     adj : accumulating and becoming more intense; "the deepening
           gloom"; "felt a deepening love"; "the gathering
           darkness"; "the thickening dusk" [syn: {deepening(a)},
           {gathering(a)}, {thickening(a)}]
     n : a process of becoming deeper and more profound