noun, plural six·ties.
- a cardinal number, ten times six.
- a symbol for this number, as 60 or LX.
- a set of this many persons or things.
- sixties, the numbers, years, degrees, or the like, from 60 through 69, as in referring to numbered streets, indicating the years of a lifetime or of a century, or noting degrees of temperature: Her grandfather is in his late sixties. The temperature is in the low sixties.