The Collaborative International Dictionary of English v.0.48:

Pentose \Pen"tose\, n. [Penta- + -ose.] (Chem.)
   Any of a group of sugars of the formula C5H10O5, such as as
   arabinose or ribose; -- so called from the five carbon
   atoms in the molecule. They are not fermented by yeast.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Xylose \Xy"lose\, n. [Pref. xylo- + -ose.] (Chem.)
   An unfermentable sugar of the pentose class, C5H10O5,
   formed by the hydrolysis of xylan; wood sugar.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Arabinose \Ar"a*bin*ose`\, n. (Chem.)
   A sugar of the composition C5H10O5, obtained from cherry
   gum by boiling it with dilute sulphuric acid.
   [1913 Webster]