see-saw

n. 1 a long plank balanced on a central support, for children to sit on at each end and move up and down alternately. B this game. 2 up-and-down or to-and-fro motion. 3 close contest with alternating advantage. v. 1 play on a see-saw. 2 move up and down. 3 vacillate in policy, emotion, etc. adj. & adv. With up-and-down or backward-and-forward motion. [reduplication of *saw1]