long-standing

adjective2

1. •
   Having existed for a long time; of long standing (duration).

   • In saying this Lenin was only repeating his long-standing belief that it was none of the people's business to decide what its interests were. — 1978
2. •
   Having been done for long enough time to become convention.

   • Long-standing custom calls for referring to the town chairman as mayor, even though we don't have a mayor.