sunset sun‧set [ˈsʌnset] adjective [only before a noun]
1. ECONOMICS no longer very profitable or important and based on old Technologies:
• As their profit levels fall, these new industries, in their turn, will become sunset sectors.
2. LAW sunset rules or laws are ones which cancel rules or laws that were made in the past:
• The new sunset law will eliminate statutes that are more than 10 years old.
• The sunset provisions will cancel most tax increases since June 30.
Financial and business terms. 2012.