■ noun
1》 a long plank balanced on a fixed support, on each end of which children sit and move up and down by pushing the ground alternately with their feet.
2》 a situation characterized by rapid, repeated changes from one state or position to another.
■ verb change rapidly and repeatedly from one state or position to another and back again.
Origin
C17 (orig. used by sawyers as a rhythmical refrain): reduplication of the verb saw 1 .