noun
companion; fellow attendee; person sitting next to one
Refers to someone who shares the same seat, table, or attendance at an event. The specific nuance depends on context: a companion at a gathering, a fellow participant, or simply the person seated beside you.
会議では、隣の同席者と名刺を交換した。
At the meeting, I exchanged business cards with the person sitting next to me.
結婚式の同席者と楽しく話した。
I enjoyed talking with my fellow attendees at the wedding reception.