pentad

A group of five.

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.

The number five, in the abstract: a set of five things considered together: as, the Pythagorean pentad: correlated with monad, dyad, triad, tetrad, etc.

Specifically A period of five consecutive years.

In chem., an element one atom of which will combine with five univalent atoms or radicals; a pentavalent element.

Having the valence of a pentad.

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.

Any grouping of five things.

a group or series of five things

the cardinal number that is the sum of four and one