[1] : The Collaborative International Dictionary of English v.0.48

tetrad \tet"rad\, n. l. tetras, -adis, gr. ?, ?: cf. f.
   t'etrade.
   1. the number four; a collection of four things; a
      quaternion.
      1913 webster

   2. chem. a tetravalent or quadrivalent atom or radical; as,
      carbon is a tetrad.
      1913 webster tetradactyl

[2] : WordNet (r) 2.0

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
see also:
four 4 iv quatern quaternion quaternary 
quaternity quartet quadruplet foursome little joe 

Tetrad >> T Words
Tetrad, definition of term: Tetrad
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