from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A person sitting next to another on a conveyance such as an airplane: "His seatmate was a gray-haired woman with glasses” ( Anne Tyler).
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One who shares a seat (such as a bench or other surface that seats more than one).
- n. One who sits next to another.
seat + mate (Wiktionary)