Meaning

noun a plaything consisting of a board balanced on a fulcrum; the board is ridden up and down by children at either end

verb ride on a plank

verb move up and down as if on a seesaw

originProbably a frequentative imitative of rhythmic back-and-forth, up-and-down or zigzagging motion, such as teeter-totter, zigzag, flip-flop, ping pong, etc., under the umbrella term of reduplication; also likely influenced by the verbs see and saw of either present or past tense.

Etymology from Wiktionary, CC BY-SA 3.0