The Collaborative International Dictionary of English v.0.48:

Saccharomyces \Sac`cha*ro*my"ces\, n. [NL., fr. Gr. ? sugar + ?,
   ?, a fungus.] (Biol.)
   A genus of budding fungi, the various species of which have
   the power, to a greater or less extent, or splitting up sugar
   into alcohol and carbonic acid. They are the active agents in
   producing fermentation of wine, beer, etc. Saccharomyces
   cerevisiae is the yeast of sedimentary beer. Also called
   Torula.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Saccharomyces
    n 1: single-celled yeasts that reproduce asexually by budding;
         used to ferment carbohydrates [syn: Saccharomyces, genus
         Saccharomyces]