What does “sunset” mean when used as a verb? [duplicate]

Solution 1:

It is a legal term, and it is used to refer to the expiration (an end) to a legal act ( law, provisions etc):

Sunset :

• (Law) The automatic expiration of a statutory provision on a previously established date, in the absence of reauthorization:
  • The law's sunset was July 1.

To sunset ( v.int.):

• To provide for the expiration of (a program or agency) by means of a sunset provision.

(TFD)

Sunset clause or sunset provision :

• (mainly US & Canadian) a provision of a law that it will automatically be terminated after a fixed period unless it is extended by law. ( Collins)!

Ngram shows that the expression Sunset Law can be traced back to the end of the 19th century and that it became more common usage from the 70s.

Sunset Law:

a law which will be discontinued, a law which will be eliminated, a statute which automatically ends, a statute which automatically terminates, a statute which expires, a statute which will cease, ending law, exxiring law, statute with a fixed lifespan, terminating law

Solution 2:

From Wiktionary:

(business, politics, transitive) To phase out.

It does mean to put something to an end, but not immediately. Just like how a sunset, the end of a day, isn't sudden.

And the noun being used here means "the act of sunsetting".

These usages are somewhat law-speak or business-speak, which could explain why it's not in the dictionary you used.

Solution 3:

It means "to [plan to] bring something to an end"; I've only noticed it being used in discussions about political acts / laws.

"In public policy, a sunset provision or clause is a measure within a statute, regulation or other law that provides that the law shall cease to have effect after a specific date, unless further legislative action is taken to extend the law."

http://en.wikipedia.org/wiki/Sunset_provision