tetrad Meaning, Definition & Usage

  1. noun the cardinal number that is the sum of three and one
    quaternity; quadruplet; foursome; Little Joe; IV; four; quaternion; quatern; quaternary; quartet; 4.

WordNet

Tet"rad noun
Etymology
L. tetras, -adis, Gr. , : cf. F. tétrade.
Definitions
  1. The number four; a collection of four things; a quaternion.
  2. (Chem.) A tetravalent or quadrivalent atom or radical; as, carbon is a tetrad.

Webster 1913