endurance continuance durability continuation persistence duration continuousness abidance ceaselessness constancy prolongation subsistence permanence stability protraction extension steadiness perpetuity succession stamina survival vitality longevity lastingness perpetuation preservation everlastingness durableness sustaining imperishability maintenance immutability changelessness endlessness propagation furtherance sustenance tenacity continuing prolonging persisting enduring perpetuating protracting maintaining preserving augmenting resilience assiduity sequel supplement postscript continuum production line increase immortality dependability permanency fixity increasing producing finality fixedness indestructibility eternality persistency solidity perenniality unchangeableness immovability unchangeability remorselessness eternity relentlessness intensity upholding sustainment sustention sustentation lasting perseverance invariability existence regularity uniformity evenness being invariableness consistency firmness timelessness agelessness lengthening intentness doggedness reliability faithfulness congruity resoluteness