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pentad

[pen-tad] /ˈpɛn tæd/
noun
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.
Origin
1645-1655
1645-55; < Greek pentad- (stem of pentás) group of five. See pent(a)-, -ad1
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for pentad

pentad

/ˈpɛntæd/
noun
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
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
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Word Origin and History for pentad
n.

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.

Online Etymology Dictionary, © 2010 Douglas Harper
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Word Value for pentad

9
11
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