Oligo(few)saccharide(sugar): A carbohydrate mol­ecule composed of 3–20 monosaccharides. Generally, free oligosaccharides do not quantitatively constitute a significant proportion of naturally occurring carbohydrates. Most carbohydrates that occur in nature are in the form of monosaccharides (such as blood sugar, or glucose), disaccharides (such as table sugar, or sucrose, and milk sugar, or lactose), and polysaccharides (such as starch and glycogen, polyglucose molecules, or chitin).