Source : Webster's Revised Unabridged Dictionary (1913)

Culvert \Cul"vert\ (k?l"v?rt), n. [Prob. from OF. coulouere, F.
   couloir, channel, gutter, gallery, fr. couler to flow. See
   {Cullis}.]
   A transverse drain or waterway of masonry under a road,
   railroad, canal, etc.; a small bridge.

Source : WordNet®

culvert
     n : a transverse and totally enclosed drain under a road or
         railway