/ Dictionary / Index I imperial gallon: Meaning and Definition of Find definitions for: impe'rial gal'lon Pronunciation: [key] a British gallon equivalent to 1 U.S. gallons, or 277.42 cubic inches. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. imperial eagle imperialism Related Content Daily Word Quiz: gregarious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language