Noun
The number four; a collection of four things; a quaternion.
A tetravalent or quadrivalent atom or radical; as, carbon is a tetrad.
Source: Webster's dictionary"At full maturity the tetrad reveals the metaphoric structure of the artifact as having two figures and two grounds in dynamic and analogical relationship to each other." Source: Internet
Each quadruple (tetrad) occurs 5 times. Source: Internet
McLuhan designed the tetrad as a pedagogical tool, phrasing his laws as questions with which to consider any medium: *What does the medium enhance? Source: Internet
Pollens/Microspores of Lycopersicon esculentum at coenocytic tetrad stage of development observed through oil immersion microscope; the chromosomes of what will become four pollen grains can be seen. Source: Internet
Sulcate pollen has a furrow across the middle of what was the outer face when the pollen grain was in its tetrad. Source: Internet
The orientation of furrows (relative to the original tetrad of microspores) classifies the pollen as sulcate or colpate. Source: Internet