noun
Abstract noun referring to the quality of being permanent or lasting forever. Often used in formal, legal, or philosophical contexts.
この条約は平和の恒久性を保障するものだ。
This treaty guarantees the permanence of peace.
恒久性のある解決策を模索している。
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.