The Collaborative International Dictionary of English v.0.48:

Cantar \Can"tar\, Cantarro \Can*tar"ro\, n. [It. cantaro (in
   sense 1), Sp. cantaro (in sense 2).]
   [1913 Webster]
   1. A weight used in southern Europe and East for heavy
      articles. It varies in different localities; thus, at Rome
      it is nearly 75 pounds, in Sardinia nearly 94 pounds, in
      Cairo it is 95 pounds, in Syria about 503 pounds.
      [1913 Webster]

   2. A liquid measure in Spain, ranging from two and a half to
      four gallons. --Simmonds.
      [1913 Webster]