separatrix

from WordNet (r) 3.0 (2006)

separatrix
    n 1: a punctuation mark (/) used to separate related items of
         information [syn: {solidus}, {slash}, {virgule},
         {diagonal}, {stroke}, {separatrix}]

from The Collaborative International Dictionary of English v.0.48

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.
   [1913 Webster]