Hypertext Webster Gateway: "tetrad"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Tetrad \Tet"rad\, n. [L. tetras, -adis, Gr. ?, ?: cf. F.
t['e]trade.]
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.
From WordNet (r) 1.7 (wn)
tetrad
n : the cardinal number that is the sum of three and one [syn: {four},
{4}, {IV}, {quatern}, {quaternion}, {quaternary}, {quaternity},
{quartet}, {quadruplet}, {foursome}, {Little Joe}]
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