Source : Webster's Revised Unabridged Dictionary (1913)

Curbstone \Curb"stone`\ (k?rb"st?n`), n.
   A stone ?et along a margin as a and protection, as along the
   edge of a sidewalk next the roadway; an edge stone.

   {Curbstone broker}.See under {Broker}.

Source : WordNet®

curbstone
     n : a paving stone forming part of a curb [syn: {kerbstone}]