Source : Webster's Revised Unabridged Dictionary (1913)

Deuto- \Deu"to-\or Deut- \Deut-\ (d[=u]t-)[Contr. from Gr. ?
   second.] (Chem.)
   A prefix which formerly properly indicated the second in a
   regular series of compound in the series, and not to its
   composition, but which is now generally employed in the same
   sense as bi-or di-, although little used.