indicating that a chemical compound contains oxygen, used esp to denote that a heterocyclic compound is derived from a specified compound by replacement of a carbon atom with an oxygen atom: oxazine
oxo-
combining form
1.
indicating that a chemical compound contains oxygen linked to another atom by a double bond, used esp to denote that a compound is derived from a specified compound by replacement of a methylene group with a carbonyl group: oxobutanoic acid