= Aglycone
An <aglycone> is the nonsugar partner recovered when the carbohydrate residue of a <glycoside> is removed. For the classical oxygen-linked description, IUPAC identifies that partner as the compound $\mathrm{ROH}$. The sugar-derived residue is sometimes called the <glycone>.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Section2-Carb-33.1, paragraph defining aglycone and glycone]{ref}
<Methyl α-D-glucopyranoside> supplies a concrete example. Its glycosidic attachment contains $\mathrm{OCH_3}$, so $R$ is a <methyl group>, $\mathrm{CH_3}$. The corresponding <aglycone> is <methanol>, $\mathrm{CH_3OH}$. The fragment $R$ and the compound $\mathrm{ROH}$ are different chemical objects; a label on a structural drawing should not silently replace the recovered partner molecule.
As original formula bookkeeping, combining free <glucose> with <methanol> and subtracting <water> gives the <molecular formula> $\mathrm{C_7H_{14}O_6}$ of the methyl <glycoside>. Reversing that balance accounts for the two partners of formal <hydrolysis>. It says nothing about reaction speed or the conditions needed for cleavage.
Calling a compound an <aglycone> describes its relationship to a particular <glycoside>; it does not by itself identify a biological activity. Oxygen-, nitrogen-, sulfur- and carbon-linked sugar derivatives require their corresponding attachment descriptions, so the $\mathrm{ROH}$ example should not be applied indiscriminately to every sugar-containing compound.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Sections2-Carb-33.1 and33.3–33.7: definitions and attachment-specific nomenclature]{ref}
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