see·saw 
(sēsô′)
(sēsô′)n.
1. A long plank balanced on a central fulcrum so that with a person riding on each end, one end goes up as the other goes down. Also called regionally dandle, dandle board, teedle board, teeter, teeterboard, teeter-totter, tilt1, tilting board.
2. The act or game of riding a seesaw.
3. A back-and-forth or up-and-down movement.
4. An action or process in which something repeatedly changes from one condition or situation to another: the seesaw in temperatures.
intr.v. see·sawed, see·saw·ing, see·saws
1. To play on a seesaw.
2. To move back and forth or up and down.
3. To change back and forth from one condition or situation to another: The lead seesawed for much of the tennis match.
[Reduplication of SAW1.]
Our Living Language The seesaw is known regionally by many names. In southeast New England it is called a tilt or a tilting board. Speakers in northeast Massachusetts call it a teedle board, and around Narragansett Bay it is often called a dandle or dandle board. Teeter or teeterboard is used more generally in the northeast United States, while teeter-totter, probably the most common term after seesaw, is used across the inland northern states and westward to the West Coast. Both seesaw (from the verb saw) and teeter-totter (from teeter, as in to teeter on the edge) demonstrate the linguistic process called reduplication, where a word or syllable is doubled, often with a different vowel. Reduplication is typical of words that indicate repeated activity, such as riding up and down on a seesaw.