Source : Webster's Revised Unabridged Dictionary (1913)

Broaden \Broad"en\, v. t. [imp. & p. p. {Broadened}; p. pr. &
   vb. n. {Broadening}.] [From {Broad}, a.]
   To grow broad; to become broader or wider.

         The broadening sun appears.              --Wordsworth.

Source : WordNet®

broadening
     n 1: the act of making something wider [syn: {widening}] [ant: {narrowing}]
     2: the action of making broader; "the broadening of travel"
     3: an increase in width [syn: {widening}] [ant: {narrowing}]