1 [countable] an arrangement for a seat on a plane or train, a room in a hotel, etc. to be kept for you
I'll call the restaurant and make a reservation.
We have a reservation in the name of Grant.
compare booking
2 [countable, uncountable] a feeling of doubt about a plan or an idea
synonym misgiving
I have serious reservations about his ability to do the job.
They support the measures without reservation(= completely).
3 (also reserve) [countable] an area of land in the US that is kept separate for Native Americans to live in
4 [uncountable]