perpetuity

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The quality or condition of being perpetual.
• noun Time without end; eternity.
• noun The condition of an estate that is limited so as to be inalienable either perpetually or longer than the period determined by law.
• noun An estate so limited.
• noun An annuity payable indefinitely.
• idiom (in perpetuity) For an indefinite period of time; forever.

from The Century Dictionary.

• noun The state or character of being perpetual; endless duration; continued uninterrupted existence, or duration through the ages or for an indefinite period of time: as,the perpetuity of laws and institutions.
• noun Something of which there will be no end; something lasting forever or for an indefinitely long time.
• noun In law: A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law. Pollock.
• noun Duration to all futurity; exemption from intermission or ceasing.
• noun In the doctrine of annuities, the number of years in which the simple interest of any principal sum will amount to the same as the principal itself; or the number of years' purchase to be given for an annuity which is to continue forever; also, the annuity itself.

from the GNU version of the Collaborative International Dictionary of English.

• noun The quality or state of being perpetual.
• noun Something that is perpetual.
• noun Endless time.
• noun The number of years in which the simple interest of any sum becomes equal to the principal.
• noun The number of years' purchase to be given for an annuity to continue forever.
• noun A perpetual annuity.
• noun Duration without limitations as to time.
• noun The quality or condition of an estate by which it becomes inalienable, either perpetually or for a very long period; also, the estate itself so modified or perpetuated.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable The quality or state of being perpetual; endless duration; uninterrupted existence.
• noun countable Something that is perpetual.
• noun countable, law A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law.
• noun countable, finance An annuity in which the periodic payments begin on a fixed date and continue indefinitely.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the property of being perpetual (seemingly ceaseless)