fifth

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ordinal number matching the number five in a series.
• noun One of five equal parts.
• noun One fifth of a gallon or four fifths of a quart of liquor.
• noun A tone five degrees above or below a given tone in a diatonic scale.
• noun The interval between two such tones.
• noun The harmonic combination of two such tones.
• noun The dominant of a scale or key.
• noun The Fifth Amendment. Used with the.

from The Century Dictionary.

• Next after the fourth: an ordinal numeral.
• noun The quotient of unity divided by five; one of five equal parts of anything: as, one fifth (⅕) of an acre.
• noun In music: A tone five diatonic degrees above or below any given tone.
• noun The interval between any tone and a tone five degrees distant from it.
• noun The combination of two tones distant by a fifth.
• noun In a scale, the fifth tone from the bottom; the dominant: solmizated sol, as G in the scale of C, or E in that of A.
• noun In early English law, a fifth part of the rents of the year, or of movables, or both, granted or levied by way of tax.

from the GNU version of the Collaborative International Dictionary of English.

• noun The quotient of a unit divided by five; one of five equal parts; a fifth part.
• noun (Mus.) The interval of three tones and a semitone, embracing five diatonic degrees of the scale; the dominant of any key.
• adjective Next in order after the fourth; -- the ordinal of five.
• adjective Consisting of one of five equal divisions of a thing.
• adjective (Hist.) a fanatical sect in England, of the time of the commonwealth, who maintained that there would be a fifth universal monarchy, during which Christ would reign on earth a thousand years.
• adjective a horizontal wheel or segment above the fore axle of a carriage and beneath the body, forming an extended support to prevent careening.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective The ordinal form of the number five.
• noun The person or thing in the fifth position.
• noun One of five equal parts of a whole.
• noun The fifth gear of an engine.
• noun A quantity of liquor equal to one-fifth of a gallon, or, more commonly, 750 milliliters.
• noun The musical interval between one note and another five tones higher.
• noun The fifth voice in a polyphonic melody.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun one part in five equal parts
• noun a quantity of liquor equal to one fifth of a United States gallon
• adjective coming next after the fourth and just before the sixth in position
• noun position five in a countable series of things
• noun the musical interval between one note and another five notes away from it