| continual(adjective, stable, constant, enduring, lasting) |
| continuing(adjective, continue, fundamental, permanent, operating) |
| infinite(adjective, end, limitless) |
| persisting(adjective, permanent, continuing, long-term, lifelong) |
| tough(adjective, calm, strong, solid, steady) |
| aged |
| ageless(lasting, permanent, everlasting, unending, undying) |
| continuous |
| dateless(lasting, permanent, everlasting, unending, undying) |
| endless(continuous, permanent, unlimited, everlasting, eternal) |
| immemorial(lasting, permanent, everlasting, unending, undying) |
| immortal(adjective, imperishable) |
| immutable(calm, strong, solid, substantial, constant) |
| incessant(absolute, continuous, endless, immense, permanent) |
| long-term(permanent, lifelong) |
| old(adjective, continue, permanent, continuing, recurrent) |
| perduring(tough, stable, sturdy, constant, enduring) |
| steadfast(calm, strong, solid, steady, stable) |
| steady(calm, strong, even, constant, unchanging) |
| timeless(lasting, permanent, everlasting, eternal, unending) |