1A person who lives on a reservation set apart for a particular group, especially American Indians.

2A person holding or advocating the view that certain reservations should be made with regard to the Treaty of Versailles (especially in relation to the proposed establishment of the League of Nations) before it could be ratified by the United States. Now historical.

3A person who makes reservations for customers at an airline, restaurant, etc.

That is a reservationist; holding or advocating the views of the reservationists. Now historical.