'Gallon' definitions:

Definition of 'gallon'

noun

United States liquid unit equal to 4 quarts or 3.785 liters [syn: gallon, gal]

noun

A British imperial capacity measure (liquid or dry) equal to 4 quarts or 4.545 liters [syn: gallon, Imperial gallon, congius]

From: GCIDE

Gallon \Gal"lon\, n. [OF galon, jalon, LL. galo, galona, fr. galum a liquid measure; cf. F. jale large bowl. Cf. Gill a measure.] A measure of capacity, containing four quarts; -- used, for the most part, in liquid measure, but sometimes in dry measure. [1913 Webster]
Note: The standart gallon of the Unites States contains 231 cubic inches, or 8.3389 pounds avoirdupois of distilled water at its maximum density, and with the barometer at
30 inches. This is almost exactly equivalent to a cylinder of seven inches in diameter and six inches in height, and is the same as the old English wine gallon. The beer gallon, now little used in the United States, contains 282 cubic inches. The English imperial gallon contains 10 pounds avoirdupois of distilled water at
62? of Fahrenheit, and barometer at 30 inches, equal to 277.274 cubic inches. [1913 Webster]

From: GCIDE

Imperial \Im*pe"ri*al\, a. [OE. emperial, OF. emperial, F. imp['e]rial, fr. L. imperialis, fr. imperium command, sovereignty, empire. See Empire.]
1. Of or pertaining to an empire, or to an emperor; as, an imperial government; imperial authority or edict. [1913 Webster]
The last That wore the imperial diadem of Rome. --Shak. [1913 Webster]
2. Belonging to, or suitable to, supreme authority, or one who wields it; royal; sovereign; supreme. "The imperial democracy of Athens." --Mitford. [1913 Webster]
Who, as Ulysses says, opinion crowns With an imperial voice. --Shak. [1913 Webster]
To tame the proud, the fetter'd slave to free, These are imperial arts, and worthy thee. --Dryden. [1913 Webster]
He sounds his imperial clarion along the whole line of battle. --E. Everett. [1913 Webster]
3. Of superior or unusual size or excellence; as, imperial paper; imperial tea, etc. [1913 Webster]
Imperial bushel, gallon, etc. See Bushel, Gallon, etc.
Imperial chamber, the, the sovereign court of the old German empire.
Imperial city, under the first German empire, a city having no head but the emperor.
Imperial diet, an assembly of all the states of the German empire.
Imperial drill. (Manuf.) See under 8th Drill.
Imperial eagle. (Zool.) See Eagle.
Imperial green. See Paris green, under Green.
Imperial guard, the royal guard instituted by Napoleon I.
Imperial weights and measures, the standards legalized by the British Parliament. [1913 Webster]