'oral-only' originates from English, specifically a compound of the adjective 'oral' and the adjective/adverb 'only', where 'oral' derives from Latin 'oralis' (from 'ōs, ōris' meaning 'mouth') and 'only' ultimately comes from Old English 'ān' meaning 'one' or 'alone'.

'oral-only' developed as a modern hyphenated compound in English (from earlier phrases like 'oral only' or 'orally only'), combining 'oral' (from Latin via Middle English) and 'only' (from Old English 'ān' > Middle English 'onliche'/'only').

Initially the parts meant 'of the mouth' ('oral') and 'alone/one' ('only'); over time their compound use came to specify something that exists or applies solely in spoken form, i.e. 'available or valid only by speech'.