time word · The first year of the sexagenary cycle in the traditional Chinese calendar, formed by the first heavenly stem and first earthly branch.

史书上记载，那次起义爆发于甲子年。

noun, punctuation · A complete sixty-year cycle in the Chinese calendar, often used metonymically to mean sixty years of age.

弹指一挥间，他已经度过了一个甲子。