Synonyms of long-standing

2 Syllables
deep-down, deep-dyed, fixed, chronic, lasting
3 Syllables
enduring, durable, livelong, lingering, long-lived, long-lasting, abiding, lifelong
4 Syllables
dyed-in-the-wool, perdurable, established, ever-present, immemorial, unabating, traditional
5 Syllables
long-established