- The univalent group OH, a characteristic component of bases, certain acids, phenols, alcohols, carboxylic and sulfonic acids, and amphoteric compounds.
- A compound radical (OH) which has never been isolated, but which is a factor in a vast number of chemical compounds.
- A compound radical, or unsaturated group, HO, consisting of one atom of hydrogen and one of oxygen. It is a characteristic part of the hydrates, the alcohols, the oxygen acids, etc.
- A <xref>univalent</xref> <xref>radical</xref> or <xref>functional group</xref> (–OH) in <xref>organic chemistry</xref>; present in <xref>alcohols</xref>, <xref>phenols</xref>, <xref>carboxylic acids</xref> and certain other <xref>classes</xref> of <xref>compounds</xref>.
- the monovalent group -OH in such compounds as bases and some acids and alcohols