fifth (f?fth, f?th)n.1. The ordinal number matching the number five in a series.2. One of five equal parts.3. One fifth of a gallon or four fifths of a quart of liquor.4. Music a. A tone five degrees above or below a given tone in a diatonic scale.b. The interval between two such tones.c. The harmonic combination of two such tones.d. The dominant of a scale or key.5. Fifth The Fifth Amendment. Used with the.[Middle English, from Old English f?fta; see penkwe in Indo-European roots.]fifth adv. & adj.fifth?ly adv.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.fifth (f?f?) adj (usually prenominal) a. coming after the fourth in order, position, time, etc. Often written: 5thb. (as noun): he came on the fifth. n1. (Mathematics) a. one of five equal or nearly equal parts of an object, quantity, measurement, etcb. (as modifier): a fifth part. 2. (Mathematics) the fraction equal to one divided by five ()3. (Music, other) music a. the interval between one note and another five notes away from it counting inclusively along the diatonic scaleb. one of two notes constituting such an interval in relation to the other. See also perfect9, diminished2, interval54. (Automotive Engineering) an additional high gear fitted to some motor vehiclesadv Also: fifthly after the fourth person, position, event, etcsentence connector Also: fifthly as the fifth point: linking what follows with the previous statements, as in a speech or argument[Old English f?fta]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014fifth (f?f? or, often, f??) adj. 1. next after the fourth; being the ordinal number for five. 2. being one of five equal parts. n. 3. a fifth part, esp. of one (?). 4. the fifth member of a series. 5. a fifth part of a gallon of liquor; ? of a quart (about 750 milliliters). 6. a. a musical interval encompassing five diatonic degrees. b. a tone at this interval. c. the harmonic combination of two tones a fifth apart. adv. 7. in the fifth place; fifthly. [before 1000; earlier fift, Middle English fifte, Old English f?fta] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.