Source : Webster's Revised Unabridged Dictionary (1913)

Congius \Con"gi*us\, n. [L.]
   1. (Roman Antiq.) A liquid measure containing about three
      quarts.

   2. (Med.) A gallon, or four quarts. [Often abbreviated to
      {cong.}]

Source : WordNet®

congius
     n : a British imperial capacity measure (liquid or dry) equal to
         4 quarts or 4.545 liters [syn: {gallon}, {Imperial gallon}]
     [also: {congii} (pl)]