sixth (s?ksth)n.1. The ordinal number matching the number six in a series.2. One of six equal parts.3. Music a. An interval of six degrees in a diatonic scale.b. A tone separated by this interval from a given tone.c. The harmonic combination of two tones separated by this interval.d. The sixth tone of a scale; the submediant.sixth adv. & adj.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.sixth (s?ks?) adj (Mathematics) (usually prenominal) a. coming after the fifth and before the seventh in numbering or counting order, position, time, etc; being the ordinal number of six: often written 6thb. (as noun): the sixth to go. n1. (Mathematics) a. one of six equal or nearly equal parts of an object, quantity, measurement, etcb. (as modifier): a sixth part. 2. (Mathematics) the fraction equal to one divided by six ()3. (Music, other) music a. the interval between one note and another note six 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 major14, minor4, interval5c. short for sixth chordadv Also: sixthly after the fifth person, position, etcsentence connector Also: sixthly as the sixth point: linking what follows to the previous statementsCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014sixth (s?ks?) adj. 1. next after the fifth; being the ordinal number for six. 2. being one of six equal parts. n. 3. a sixth part, esp. of one (?). 4. the sixth member of a series. 5. a. a musical interval encompassing six diatonic degrees. b. a tone at this interval. adv. 6. in the sixth place. [1520?30] sixth?ly, adv. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.