One of a large series of amorphous or crystalline substances, occurring very widely distributed in plants, rarely in animals, and regarded as influental agents in the formation and disposition of the sugars. They are frequently of a bitter taste, but, by the action of ferments, or of dilute acids and alkalies, always break down into some characteristic substance (acid, aldehyde, alcohol, phenole, or alkaloid) and glucose (or some other sugar); hence the name. They are of the nature of complex and compound ethers, and ethereal salts of the sugar carbohydrates.  [1913 Webster]