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Adjective: long-lasting  long'lãs-ting [N. Amer], lóng'lãs-ting [Brit]
  1. Existing for a long time
    "a long-lasting friendship";
    - durable, lasting, long-lived

See also: long, stable

Antonym: ephemeral, fugacious, here today and gone tomorrow [informal], here today gone tomorrow [informal], passing, short-lived, transient, transitory