Abstract noun referring to the quality of being permanent or lasting forever. Often used in formal, legal, or philosophical contexts.
This treaty guarantees the permanence of peace.
We are seeking a solution with perpetuity.
恒久 is a noun or na-adjective meaning 'permanent' or 'everlasting'. 恒久性 adds the suffix 性 to explicitly denote the property or quality of permanence.
Compound of 恒久 (permanent, everlasting) and 性 (nature, quality). The exact historical derivation is uncertain, but the word follows a common pattern of forming abstract nouns from adjectives or adjectival nouns.