'once-only' originates from English, specifically from the words 'once' and 'only', where 'once' meant 'one time' and 'only' meant 'single' or 'sole'.

'once' developed from Old English forms (related to ān, meaning 'one') and came to mean 'on one occasion'; 'only' developed from Old English 'ānlic'/'anlic' (meaning 'single, sole'); these modern words were later combined into the compound 'once-only'.

Initially the components meant 'one time' and 'single'; as a compound, the meaning has remained essentially 'for one occasion or use only'.