What does "seesaw" mean?

Additional senses

1. 2.A vibratory or reciprocating motion. He has been arguing in a circle; there is thus a seesaw between the hypothesis and fact. Sir W. Hamilton.
2. 3.(Whist.) Same as Crossruff.
3. 4.To move with a reciprocating motion; to move backward and forward, or upward and downward.
4. 5.To cause to move backward and forward in seesaw fashion. He seesaws himself to and fro. Ld. Lytton.
5. 6.Moving up and down, or to and fro; having a reciprocating motion.