the state or character of being perpetual (often prec. by in )

to desire happiness in perpetuity.

endless or indefinitely long duration or existence; eternity.

something that is perpetual.

an annuity paid for life.

Law . an interest under which property is less than completely alienable for longer than the law allows.

noun

ceaselessness , eternality , eternalness , eternity , everlastingness , world without end , infinity , sempiternity