noun
permanence; permanency
Abstract noun referring to the quality or state of being permanent, enduring, or lasting forever. Often used in formal or technical contexts.
この素材の永久性は科学的に証明されている。
The permanence of this material has been scientifically proven.
愛の永久性
Many people believe in the permanence of love.
恒久性 also means 'permanence' but is less common and often used in legal or political contexts (e.g., 恒久平和). 永久性 is broader and more general.
Compound of 永久 (えいきゅう, 'eternity') and the suffix 性 (せい, '-ness, -ity'), forming an abstract noun meaning 'permanence'.