perpetuity

Concise Oxford English Dictionary © 2008 Oxford University Press:
perpetuity /pəːpɪˈtjuːɪti/

▶noun (pl. perpetuities)

• 1 the state or quality of lasting forever.

• 2 a bond or other security with no fixed maturity date.

• 3 Law a restriction making an interest in land inalienable perpetually or for a period beyond certain limits fixed by law.