congius

WordNet 3.6
 n congius a British imperial capacity measure (liquid or dry) equal to 4 quarts or 4.545 liters
 ***
Webster's Revised Unabridged Dictionary

 Congius (Med) A gallon, or four quarts.
 Congius (Roman Antiq) A liquid measure containing about three quarts.
 ***
Century Dictionary and Cyclopedia

 n congius A measure of capacity among the ancient Romans, the eighth part of the amphora. The standard congius of Vespasian is extant in good preservation. It contains 3,377 liters, or 0.892 of a United States (old wine) gallon. Yet most authorities, on theoretical grounds, suppose a mistake to have been made in the construction of this standard, and that it ought to have contained only 3,275 liters, or 0.865 of a United States gallon. It has also been maintained that the construction of this standard marked an increase of 2 per cent, in the Roman measures of capacity.
 n congius In pharmacy, a gallon.
 ***
Webster's Revised Unabridged Dictionary
L
In literature:
One metreta is larger than onesixth of a congius.
"De Re Metallica" by Georgius Agricola
***