[ pen-tad ]
/ ˈpɛn tæd /


a period of five years.
a group of five.
the number five.
Chemistry. a pentavalent element or group.
Climatology. a period of five consecutive days.

Origin of pentad

1645–55; < Greek pentad- (stem of pentás) group of five. See pent(a)-, -ad1 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for pentad

British Dictionary definitions for pentad


/ (ˈpɛntæd) /


a group or series of five
the number or sum of five
a period of five years
chem a pentavalent element, atom, or radical
meteorol a period of five days

Word Origin for pentad

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.

Online Etymology Dictionary, © 2010 Douglas Harper