(n.) The period of time during which anything lasts\; continuance in time; the portion of time during which anything exists.

abidingness age antiquity changelessness chronology constancy continuance continuation continuity defeat of time defiance of time diuturnity durability durableness duree endurance firmness fixedness frozenness hardening immobility immovability immovableness immutability invariability invariableness inveteracy lastingness long standing long-lastingness long-livedness longevity maintenance perdurability perennation period permanence permanency perpetualness perpetuity persistence persistency psychological time quiescence rigidity run solidity space space-time span spell stability standing stasis steadfastness survival survivance tense tenure term the future the past the present tide time timebinding torpor unchangeability unchangingness while