long-standing

/L AO1 NG S T AE0 N D IH0 NG/
adjective
  1. 1

    Having existed for a long time.

  2. 2

    Having been done for long enough time to become convention.

    โ€œLong-standing custom calls for referring to the town chairman as mayor, even though we don't have a mayor.โ€

Source: https://en.wiktionary.org/wiki/long-standing