'O-deethylate' originates from modern chemical nomenclature, composed of the letter 'O' (denoting an oxygen atom), the prefix 'de-' from Latin meaning 'remove' or 'from', 'ethyl' from French 'éthyl' ultimately from Greek 'aithēr' meaning 'ether', and the verb-forming suffix '-ate' used in New Latin/English to mean 'to make or act on'.

'O-deethylate' developed from earlier forms such as 'de-ethylate' or 'deethylate' used in 19th–20th century chemical and pharmacological literature; the current hyphenated form emphasizes the atom-specific notation 'O-' (oxygen) combined with 'deethylate'.

Initially used broadly to mean 'remove an ethyl group' (de-ethylation), it became more specific in biochemical nomenclature to mean removal of an ethyl group specifically attached to an oxygen atom ('O-deethylation').