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  1  definition  found 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
  Dyas  \Dy"as\,  n.  [L.  dyas  the  number  two.]  (Geol.) 
  A  name  applied  in  Germany  to  the  Permian  formation,  there 
  consisting  of  two  principal  groups.