Any monosaccharide sugar containing five atoms of carbon per molecule

• A carbohydrate

Wikipedia Word definitions in Wikipedia
A pentose is a monosaccharide with five carbon atoms . Pentoses are organized into two groups. Aldopentoses have an aldehyde functional group at position 1. Ketopentoses have a ketone functional group in position 2 or 3.

Wiktionary Word definitions in Wiktionary
n. (context carbohydrate English) A sugar or saccharide containing five carbon atoms.

WordNet Word definitions in WordNet
n. any monosaccharide sugar containing five atoms of carbon per molecule

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
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.