The word "yo-yo" is a direct borrowing from the Ilocano language of the Philippines, where "yóyo" referred to the toy. It was popularized in the United States in the 1920s by Filipino immigrant Pedro Flores and later marketed by Donald F. Duncan. The term itself is likely a reduplication, a common linguistic feature, and its adoption into English represents a classic example of a trademark becoming a generic term. The modern verb sense, meaning to fluctuate, is a metaphorical extension from the toy's characteristic up-and-down motion.

The word "yo-yo" is a reduplication, a linguistic process where a word or part of a word is repeated. It is not productively built from distinct, separable morphemes in English. It originated as a trademark name.