Simple Definition of seatmate
: a person who sits next to you on a bus, airplane, etc.
Full Definition of seatmate
: one with whom one shares a seat (as in a vehicle with double or paired seats)
Examples of seatmate in a sentence
My seatmate on the flight to Rome was very friendly.
First Known Use of seatmate
Seen and Heard
What made you want to look up seatmate? Please tell us where you read or heard it (including the quote, if possible).