To expire on a previously established date, as a statutory provision, To provide for the expiration of (a program or agency) by means of a sunset provision, verb_ business, politics, transitive To phase out, adjective_ Law Providing for an automatic expiration, providing for termination, of a declining industry or technology, noun_ the daily event of the sun sinking below the horizon, attributively Having a set termination date, The time of day when the sun disappears below the western horizon