1.nounA toy consisting of a spheroidal or cylindrical spindle having a circular groove in which string is wound; it is used by holding the string in the fingers and reeling the spindle up and down by movements of the wrist.
"I bought a yo-yo from the toy store yesterday."
2.nounA volatile market that moves up and down.
3.nounSomeone who vacillates.
4.nounA cloth rosette formed by gathering the outside edge of a circle of fabric in toward the centre using a running stitch.
5.nounA foolish, annoying or incompetent person.
"It is hard to watch the management for very long and not conclude that the place is run by a bunch of yo-yos."