yo-yo

(trademark in the UK)

noun (plural yo-yos)

1》 a toy consisting of a pair of joined discs with a deep groove between them in which string is attached and wound, which can be spun alternately downward and upward by its weight and momentum as the string unwinds and rewinds.

    ↘a thing that repeatedly fluctuates.

2》 informal, chiefly N. Amer. a stupid, insane, or unpredictable person.

verb (yo-yoes, yo-yoing, yo-yoed) move up and down repeatedly; fluctuate.

Origin

1915: prob. ult. from a lang. of the Philippines.