pentosan

from The Collaborative International Dictionary of English v.0.48

Pentosan \Pen"to*san\, n. Also -sane \-sane\ [From {Pentose}.]
   (Chem.)
   One of a class of substances (complex carbohydrates widely
   distributed in plants, as in fruits, gums, woods, hay, etc.)
   which yield pentoses on hydrolysis.
   [Webster 1913 Suppl.]