Pronunciation: (sun'set"),[key] —n. 1. the setting or descent of the sun below the horizon in the evening.
2. the atmospheric and scenic phenomena accompanying this.
3. the time when the sun sets.
4. the close or final stage of any period.
—adj. 1. (of an industry, technology, etc.) old; declining: sunset industries. 2. of, pertaining to, or characteristic of a sunset law: to add sunset restrictions to a bill.