glyc(o)-

Also gluc(o)‑.

Sugar.

Greek glukus, sweet.

The first substance named using glyco‑ was glycerine (now more usually glycerol, especially in scientific contexts), because it tasted sweet. Gluco‑ was first used in the name of the important sugar glucose.

In modern chemistry glyco‑ is more common than gluco‑, and refers to the sugars, which in combination make up the carbohydrates and starches. So a glycoside is a compound produced from any of the simple sugars, a glycogen is a substance deposited in bodily tissues as a store of carbohydrates and a glycoprotein is a protein with carbohydrate groups attached.

Some compounds in gluco‑ relate to any sugar, such as glucocorticoid, one of a group involved in the metabolism of carbohydrates. However, most current words including it refer specifically to glucose: a glucoside is a glycoside that derives from glucose alone, a glucan is a complex sugar containing only glucose units, and glucagon is a hormone in the pancreas that promotes the breakdown of glycogen to glucose.