What is "pentosan"

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.

n. (context carbohydrate English) Any polysaccharide composed of pentoses