From Middle English son-sett, Sonne set, equivalent to sun +‎ set. In Gower's Confessio Amantis, before 1393.^[1]

• IPA^(key): /ˈsʌnˌsɛt/

• Audio (US):

  (file)

• Rhymes: -ʌnsɛt

sunset (countable and uncountable, plural sunsets)

1. The moment each evening when the sun disappears below the western horizon.

   at sunset

   • 1829, Edgar Allan Poe, “Tamerlane”, in Al Aaraaf, Tamerlane and Minor Poems:

     ’Twas sunset: when the sun will part
     There comes a sullenness of heart
     To him who still would look upon
     The glory of the summer sun.

2. The changes in color of the sky before and after sunset.
3. (figuratively) The final period of the life of a person or thing.

   one's sunset years

   • 1799, Thomas Campbell, Pleasure of Hope:

     'Tis the sunset of life gives me mystical lore.

4. (attributively) A set termination date.

   The tax increase legislation included a sunset clause requiring renewal to prevent the tax increase from expiring.

5. The region where the sun sets; the west.

• (time): dusk, sundown (US), nightfall, twilight; see also Thesaurus:dusk
• (change in color of the sky at sunset):
• (final period of life): end, final act, swansong
• (attributively: of or relating to the final period of life): last, terminal, twilight

• sunrise

sunset (third-person singular simple present sunsets, present participle sunsetting, simple past and past participle sunsetted)

1. (business, politics, transitive) To phase out.

   We’ll be sunsetting version 1.9 of the software shortly after releasing version 2.0 next quarter.

   • 2011 April 19, Sumit Paul-Choudhury, “Digital legacy: The fate of your online soul”, in NewScientist‎^[1]:

     Last December, Yahoo announced plans to “sunset” more well-known services, including the pioneering social bookmarking service del.icio.us.

• moonset

• unsets