'reservationist' originates from the noun 'reservation' (from Latin 'reservare') combined with the agentive suffix '-ist' (from Greek '-istes' via Latin/French), where Latin 'reservare' meant 'to keep back, retain' and the suffix '-ist' denotes 'a person who practices or is concerned with'.

'reservation' came into English via Old French 'reservacion' (from Latin 'reservatio') and developed in Middle and Early Modern English as 'reservation'; the modern English occupational formation 'reservationist' was created by adding the productive suffix '-ist' to denote a person performing that action.

Initially, 'reservation' referred to the act or state of reserving; over time, adding the suffix '-ist' produced 'reservationist', which came to mean 'a person who makes or handles reservations'.