Source : Webster's Revised Unabridged Dictionary (1913)

Cobblestone \Cob"ble*stone`\, n.
   A large pebble; a rounded stone not too large to be handled;
   a small boulder; -- used for paving streets and for other
   purposes.

Source : WordNet®

cobblestone
     n : rectangular paving stone with curved top; once used to make
         roads [syn: {cobble}, {sett}]