seatmate

[ seet-meyt ]

/ ˈsitˌmeɪt /

a person who shares a seat or occupies the seat next to oneself on a bus, plane, etc.

Origin of seatmate

An Americanism dating back to 1855–60; seat + mate¹

But then, when one sparkled bustier passed her on the runway, she pointed and whispered to her seatmate: “Now, that I could wear.”

Phaedra Parks of ‘Real Housewives of Atlanta’ at Jeremy Scott NYFW Show |Isabel Wilkinson |February 16, 2012 |DAILY BEAST
Bessie's seatmate, a girl named Nora, about Bessie's own age, was very mischievous.

The value of a praying mother |Isabel C. Byrum
Bud turned to his seatmate, a youngster who was tackling the complexities of the eighth grade for the third time.

The Black Fawn |James Arthur Kjelgaard
"Sure," asserted the other, delighted to be able to surprise her seatmate.

Elsie Marley, Honey |Joslyn Gray

I was her seatmate during all of the remainder of that school year.

A Preliminary Study of the Emotion of Love between the Sexes |Sanford Bell
A number greeted Toms seatmate as an old friend and our hero was introduced to them.

Tom Fairfield's Schooldays |Allen Chapman