Source : Webster's Revised Unabridged Dictionary (1913)

Boulevard \Bou"le*vard`\, n. [F. boulevard, boulevart, fr. G.
   bollwerk. See {Bulwark}.]
   1. Originally, a bulwark or rampart of fortification or
      fortified town.

   2. A public walk or street occupying the site of demolished
      fortifications. Hence: A broad avenue in or around a city.

Source : WordNet®

boulevard
     n : a wide street or thoroughfare [syn: {avenue}]