seatmate

noun

1. One who shares a seat (such as a bench or other surface that seats more than one).
2. One who sits next to another.

   “My seatmate on the airplane snored incessantly.”

   “The Buzzis' older son, Rocco, and I had been high school buddies, then roommates at BU, seatmates at Sox games.”

   “Last month, the cryptographer and coder known as Moxie Marlinspike was getting settled on an airplane when his seatmate, a Midwestern-looking man in his sixties, asked for help.”

   “Several years ago, I was sitting on a flight to San Francisco, when my seatmate, a man a little older than me, struck up a conversation. Perhaps you hate it when that happens; I love it.”