I. -ˌset noun
Date: 14th century
1. : the apparent descent of the sun below the horizon ; also : the accompanying atmospheric effects
2. : the time when the upper limb of the sun disappears below the horizon as a result of the diurnal rotation of the earth
3. : a period of decline ; especially : old age
II. adjective
Date: 1976
: stipulating the periodic review of government agencies and programs in order to continue their existence
sunset laws