From Longman Dictionary of Contemporary Englishseesawsee‧saw1 /ˈsiːsɔː $ -sɒː/ noun [countable] 1 
DHTa piece of equipment that children play on, made of a board that is balanced in the middle, so that when one end goes up the other goes down SYN teeter-totter American English2 a repeated movement from one state or condition to another and back again SYN oscillation
DHTa piece of equipment that children play on, made of a board that is balanced in the middle, so that when one end goes up the other goes down SYN teeter-totter American English2 a repeated movement from one state or condition to another and back again SYN oscillationExamples from the Corpus
seesaw• It should be a seesaw affair.• As soon as they try to see Agnes's mind it sinks down and up pops Perdita like a seesaw.• Like the other end of a seesaw, Agnes rose. ` Where's Magrat?• So, lie flat on your back over the pivot on a seesaw, and arrange yourself so that it balances.• Which boy on the seesaw is heavy?• It is rather like warfare, the seesaw of offensive and defensive, of tank armour and the high-velocity penetrating bullet.seesawseesaw2 verb [intransitive] CHANGE FROM ONE THING TO ANOTHERto keep changing from one state or condition to another and back again Before the election, the president seesawed in the polls.→ See Verb tableExamples from the Corpus
seesaw• His fortunes, internationally and domestically, as player and captain, seesawed alarmingly during the 1991-92 season.• The Dow Jones Industrial Average seesawed before closing down 21. 32 at 5066. 9.• Mickelson never was really in it, as his 2 birdies and 2 bogeys kept him seesawing between 5 and 6 under.• The Dow Jones Industrial Average fell 21. 32 to 5066. 9 after seesawing for most of the session.• Other reluctant players include squirrels, coyotes and ravens, all of whom seesaw in synchrony.• Stock prices seesawed throughout the morning.Origin seesaw1 (1600-1700) Probably from → SAW2 