The Collaborative International Dictionary of English v.0.48:

Perpetuity \Per`pe*tu"i*ty\, n. [L. perpetuitas: cf. F.
   perp['e]tuit['e].]
   1. The quality or state of being perpetual; as, the
      perpetuity of laws. --Bacon.
      [1913 Webster]

            A path to perpetuity of fame.         --Byron.
      [1913 Webster]

            The perpetuity of a single emotion is insanity. --I.
                                                  Taylor.
      [1913 Webster]

   2. Something that is perpetual. --South.
      [1913 Webster]

   3. Endless time. "And yet we should, for perpetuity, go hence
      in debt." --Shak.
      [1913 Webster]

   4. (Annuities)
      (a) The number of years in which the simple interest of
          any sum becomes equal to the principal.
      (b) The number of years' purchase to be given for an
          annuity to continue forever.
      (c) A perpetual annuity.
          [1913 Webster]

   5. (Law)
      (a) Duration without limitations as to time.
      (b) 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.
          [1913 Webster]

WordNet (r) 3.0 (2006):

perpetuity
    n 1: the property of being perpetual (seemingly ceaseless) [syn:
         perpetuity, sempiternity]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "perpetuity":
   abidingness, age, all-comprehensiveness, all-inclusiveness,
   antiquity, boundlessness, ceaselessness, chattering, constancy,
   constant flow, continualness, continuance, continuity,
   countlessness, defeat of time, defiance of time, distance,
   diuturnity, durability, durableness, duration, endlessness,
   endurance, eternity, exhaustlessness, extension, extent, forever,
   illimitability, immeasurability, immensity, incalculability,
   incessancy, incomprehensibility, inexhaustibility, infiniteness,
   infinitude, infinity, innumerability, interminability, lastingness,
   length, lengthiness, limitlessness, linear measures, long standing,
   long time, long-lastingness, long-livedness, longevity, longitude,
   longness, maintenance, measure, measurelessness, mileage,
   noninterruption, numberlessness, oscillation, overall length,
   perdurability, perennation, permanence, persistence, pulsation,
   quick fire, rapid fire, rapid recurrence, rapid succession,
   rapidity, reach, regularity, repetition, span, stability, staccato,
   standing, steadfastness, steadiness, stretch, stuttering, survival,
   survivance, sustainment, tattoo, termlessness, timelessness,
   unintermission, uninterruption, universality, unmeasurability,
   vibration, world without end, yardage



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PERPETUITY, estates. Any limitation tending to take the subject of it out of
commerce for a longer period than a life or lives in being, and twenty-one
years beyond; and in case of a posthumous child, a few months more, allowing
for the term of gestation; Randall on Perpetuities, 48; or it is such a
limitation of property as renders it unalienable beyond the period allowed
by law. Gilbert on Uses, by Sugden, 260, note.
     2. Mr. Justice Powell, in Scattergood v. Edge, 12 Mod. 278,
distinguished perpetuities into two sorts, absolute and qualified; meaning
thereby, as it is apprehended, a distinction between a plain, direct and
palpable perpetuity, and the case where an estate is limited on a
contingency, which might happen within a reasonable compass of time, but
where the estate nevertheless, from the nature of the limitation, might be
kept out of commerce longer than was thought agreeable to the policy of the
common law. But this distinction would not now lead to a better
understanding or explanation of the subject; for whether an estate be so
limited that it cannot take effect, until a period too much protracted, or
whether on a contingency which may happen within a moderate compass of time,
it equally falls within the line of perpetuity and the limitation is
therefore void; for it is not sufficient that an estate may vest within the
time allowed, but the rule requires that it must. Randall on Perp. 49. Vide
Cruise, Dig. tit. 32, c. 23; 1 Supp. to Ves. Jr. 406; 2 Ves. Jr. 357; 3
Saund. 388 h. note; Com. Dig. Chancery, 4 G 1; 3 Chan. Cas. 1; 2 Bouv. Inst.
n. 1890.