Dictionary
sunset 
/ˈsʌnˌsɛt/
lastterminaltwilightendfinal act
noun
◦ The time of day when the sun disappears below the western horizon.
◦ The changes in color of the sky at sunset.
◦ The final period of the life of a person or thing.
one's sunset years
◦ Having a set termination date.
The tax increase legislation included a sunset clause requiring renewal to prevent the tax increase from expiring.
◦ The region where the sun sets; the west.
verb
◦ To phase out.
We'll be sunsetting version 1.9 of the software shortly after releasing version 2.0 next quarter.