Source : Webster's Revised Unabridged Dictionary (1913)

Separatrix \Sep`a*ra"trix\, n.; pl. L. {-trices}, E. {-trixes}.
   [L., she that separates.] (Arith.)
   The decimal point; the dot placed at the left of a decimal
   fraction, to separate it from the whole number which it
   follows. The term is sometimes also applied to other marks of
   separation.

Source : WordNet®

separatrix
     n : a punctuation mark (/) used to separate related items of
         information [syn: {solidus}, {slash}, {virgule}, {diagonal},
          {stroke}]
     [also: {separatrices} (pl)]