immarcescible
Permanent, enduring; that does not perish.
rare
I did not think to see them once again, / For what could bring into an old woman's dream / Canova's immarcescible marble lovers?
Where it comes from
From Middle French inmarcessible (1482), later immarcescible (“that does not shrivel" or "that does not perish”), from Latin immarcescibilis (“unfading”).
Adapted from the Wiktionary entry immarcescible (CC BY-SA 4.0).