From WordNet (r) 3.0 (2006) [wn]:
boulevard
n 1: a wide street or thoroughfare [syn: avenue, boulevard]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Boulevard \Bou"le*vard`\, n. [F. boulevard, boulevart, fr. G.
bollwerk. See Bulwark.]
[1913 Webster]
1. Originally, a bulwark or rampart of fortification or
fortified town.
[1913 Webster]
2. A public walk or street occupying the site of demolished
fortifications. Hence: A broad avenue in or around a city.
[1913 Webster]