yo-yo

n. & v.
—n. (pl. yo-yos)
1 a toy consisting of a pair of discs with a deep groove between them in which string is attached and wound, and which can be spun alternately downward and upward by its weight and momentum as the string unwinds and rewinds.
2 a thing that repeatedly falls and rises again.
—v.intr. (yo-yoes, yo-yoed)
1 play with a yo-yo.
2 move up and down; fluctuate.
Etymology: 20th c.: orig. unkn.