Source : Webster's Revised Unabridged Dictionary (1913)

Furlong \Fur"long\, n. [OE. furlong, furlang, AS. furlang,
   furlung, prop., the length of a furrow; furh furrow + lang
   long. See {Furrow}, and {Long}, a.]
   A measure of length; the eighth part of a mile; forty rods;
   two hundred and twenty yards.

Source : WordNet®

furlong
     n : a unit of length equal to 220 yards