Synonyms for Longstanding (same or very similar meaning)
WordNet sense 1 (primarily temporal sense; being or indicating a relatively great or greater than average duration or passage of time or a duration as specified):
long
WordNet sense 2 (having existed or continued for a long time):
long-standing
WordNet sense 3 (consisting of or derived from tradition):
traditional
From the ODE community, based on WordNet
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