seesaw
Definitions
A long plank balanced on a central support, on which two people sit at opposite ends and move up and down in turn.
A situation or state characterized by repeated back-and-forth movement or fluctuation between two conditions.
Examples
The children took turns going up and down on the playground seesaw.
The stock market has been on a seesaw lately, fluctuating between gains and losses.
They sat on opposite ends of the seesaw to keep it perfectly balanced.
Synonyms
teeter-totter fluctuate oscillate vacillate waver swing alternate