–noun.
1. the going down of the sun; last appearance of the sun in the evening: »
After sunset, the horizon burned and glowed with rich crimson and orange lustre (Hawthorne).
2. the time when the sun goes down; close of day. SYNONYM(S): sundown.
3. the display of light and color in the sky at this time: »
Then in the sunset's flush they went aloft (John Masefield).
4. Figurative. decline or close, especially of a period of prosperity or the like: »
the sunset of life (Thomas Campbell).
–transitive verb.
to phase out or end the use of: »
The International Joint Commission…suggested that its patrons “sunset”…persistent toxic chemicals (Science News).
–intransitive verb.
to cease to be in effect: »
The rule is scheduled to sunset in ten years.
Useful english dictionary. 2012.