What does hydroxy mean?
“Hydroxy” is a technical chemistry term used to indicate that a substance contains a hydroxyl group, written –OH, in which a hydrogen atom is bonded to an oxygen atom. It occurs as an adjective and as the combining form hydroxy-, as in hydroxyapatite, hydroxy acid, and hydroxy compound. The term is especially useful when describing the presence and chemical behaviour of an –OH group, including its capacity to donate a hydrogen bond and, in some molecules, to lose or gain a proton. It is not synonymous with “alcohol” in every context: a hydroxyl group need not be part of an alcohol molecule, although many simple compounds containing –OH are alcohols. British and American scientific usage generally follow the same conventions. Learning the word helps distinguish an atomic group from the larger molecule carrying it and provides a precise label for structures encountered in medicine, biochemistry, pharmaceuticals, and materials science.
adjective and combining formDenoting a chemical group or compound containing one or more hydroxyl groups (–OH), each consisting of hydrogen bonded to oxygen.
- Denoting or naming a chemical group, compound, or substance containing a hydroxyl group (–OH).
"The reaction occurs at a hydroxy group on the aromatic ring."
"Water molecules can form hydrogen bonds through their oxygen atoms and attached hydrogens."
"Hydroxyapatite is the mineral form of calcium phosphate found in bone and teeth."
Hydroxy is a chemical calling card: it flags the all-important –OH group, where oxygen and hydrogen meet.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hydroxy come from?
Hydroxy is a combining form built from hydro- and oxy-, drawing ultimately on Greek roots associated with water and with sharpness or acidity. The oxy- element became closely associated with oxygen in modern chemical terminology. Together, the elements developed into a way of identifying the presence of a hydroxyl group, written –OH.
Related word forms
How hydroxy is actually used
This is primarily formal scientific terminology. When attached to another chemical term, it is commonly written hydroxy- with a hyphen, as in hydroxyapatite; in established terms such as hydroxy group, it may appear unhyphenated.
Easily confused with hydroxy
Hydroxy is the adjective or combining form describing something that contains a hydroxyl group, whereas hydroxyl is the noun naming the –OH group itself.