To move backwards and forwards, like a piston.
To exchange two things, with both parties giving one thing and taking another thing.
To give something else in response (where the "thing" may also be abstract, a feeling or action) To make a reciprocal gift.
To counter, retort or retaliate.
To fit (something, especially a valve) back into its place.
To sit down again.
To provide (e.g. a room) with more, or new, seats.
To seat (someone) again, to give somebody a different seat.
To plug (something) back into its socket.