'appointment-only' originates from the combination of 'appointment' and 'only', where 'appointment' meant 'a scheduled meeting' and 'only' meant 'solely or exclusively'.

'appointment' changed from the Old French word 'apointement' and eventually became the modern English word 'appointment'.

Initially, 'appointment' meant 'an arrangement to meet someone at a particular time', and this meaning has largely remained the same in modern usage.