the cardinal quantity this is the amount of four and one
- Any element atom or radical having a valence of five or that can easily be coupled with substituted for or in contrast to five atoms of hydrogen or any other monad as nitrogen is a pentad in the ammonium compounds
- obtaining the valence of a pentad
- Any factor, atom, or radical, having a valence of five, or and this can be coupled with, substituted for, or weighed against, five atoms of hydrogen or any other monad; because, nitrogen is a pentad when you look at the ammonium compounds.
- Having the valence of a pentad.
1650s, from Greek pentas (genitive pentados) "group of five" (see five). Meaning "period of 5 years" is from 1880; meaning "period of five times" is from 1906, originally in meteorology.
Those elements which are equivalent in combining or displacing power to a single atom of hydrogen are said to be univalent or monad elements; whilst those which are equivalent to two atoms of hydrogen are termed bivalent or dyad elements; and those equivalent to three, four, five or six atoms of hydrogen triad, tetrad, pentad or hexad elements.