from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A group of five.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. a group or series of five things
from the GNU version of the Collaborative International Dictionary of English
- n. Any element, atom, or radical, having a valence of five, or which can be combined with, substituted for, or compared with, five atoms of hydrogen or other monad.
- n. Any grouping of five things.
- adj. Having the valence of a pentad.
from The Century Dictionary and Cyclopedia
- n. The number five, in the abstract: a set of five things considered together: as, the Pythagorean pentad: correlated with monad, dyad, triad, tetrad, etc.
- n. Specifically A period of five consecutive years.
- n. In chem., an element one atom of which will combine with five univalent atoms or radicals; a pentavalent element.
- n. A period of five days, introduced by Dove for use in climatological study. The pentads begin January 1–5, and continue in groups of five days each throughout the ordinary year. The twelfth pentad, from February 25-March 1, may be increased by one day, namely, February 29th, without disturbing the calendar dates of the subsequent pentads.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the cardinal number that is the sum of four and one
Greek pentas, pentad-, group of five, from pente, five; see penkwe in Indo-European roots.(American Heritage® Dictionary of the English Language, Fourth Edition)