Source : Webster's Revised Unabridged Dictionary (1913)

Arroba \Ar*ro"ba\, n. [Sp. and Pg., from Ar. arrub, ar-rubu, a
   fourth part.]
   1. A Spanish weight used in Mexico and South America = 25.36
      lbs. avoir.; also, an old Portuguese weight, used in
      Brazil = 32.38 lbs. avoir.

   2. A Spanish liquid measure for wine = 3.54 imp. gallons, and
      for oil = 2.78 imp. gallons.

Source : WordNet®

arroba
     n 1: a unit of weight used in some Spanish speaking countries
     2: a liquid measure (with different values) used in some
        Spanish speaking countries