Synonyms for Perennial (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):
longWordNet sense 2 (recurring again and again):
recurrent, repeatedWordNet sense 3 (seemingly without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series):
continualFrom the ODE community, based on WordNetadd/edit