(of a programme, agency, regulation, etc.) expire or be terminated automatically at the end of a fixed period unless renewed by legislative action

the tax cut will sunset after three years unless lawmakers extend it

the time in the evening when the sun disappears or daylight fades

sunset was still a couple of hours away

denoting a legal provision under which a programme, agency, regulation, etc., is automatically terminated at the end of a fixed period unless renewed by legislative action

the bill will have a two-year sunset clause, so the decision will need to be revisited after the next election

the fiscal stimulus is temporary, with sunset provisions built in from the beginning