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See more synonyms for pentad on Thesaurus.com
  1. a period of five years.
  2. a group of five.
  3. the number five.
  4. Chemistry. a pentavalent element or group.
  5. Climatology. a period of five consecutive days.
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Origin of pentad

1645–55; < Greek pentad- (stem of pentás) group of five. See pent(a)-, -ad1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words


Examples from the Web for pentad

Historical Examples

  • But this oddness belongs to other numbers also (pentad, heptad, &c.).


    George Grote

  • In 1820, he added to the last a pentad, so that the whole list amounted to sixty-five.

    Man and His Migrations

    R. G. (Robert Gordon) Latham

  • Five, or the pentad, is everything; it stops the power of poisons, and is dreaded by evil spirits.

  • Nitrogen in the triad condition in the amines is far less poisonous than in the pentad condition.

  • There is something to be said for this view, but on the whole the balance of the evidence is in favor of nitrogen being a pentad.

British Dictionary definitions for pentad


  1. a group or series of five
  2. the number or sum of five
  3. a period of five years
  4. chem a pentavalent element, atom, or radical
  5. meteorol a period of five days
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Word Origin

C17: from Greek pentas group of five
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for pentad


1650s, from Greek pentas (genitive pentados) "group of five" (see five). Meaning "period of five years" is from 1880; meaning "period of five days" is from 1906, originally in meteorology.

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Online Etymology Dictionary, © 2010 Douglas Harper