| impregnable(adjective, strain, firmness, labour, hardiness) |
| indestructible(adjective, strong, tough, stable, sturdy) |
| long-lasting(adjective, tough, continue, stable, enduring) |
| perennial(adjective, continue, stable, constant, stability) |
| solid(adjective, calm, strong, sound, tough) |
| perdurable(adjective, calm, strong, tough, continue) |
| abiding(adjective, calm, strong, secure, tough) |
| fixed(adjective, strong, sound, secure, tough) |
| long-lived(adjective, continue, continuing, diuturnity) |
| well-built(adjective, calm, strong, sound, secure) |
| continuing(adjective, continue, established, lasting, permanent) |
| dependable(adjective, strong, tough, firm, solid) |
| hardy(adjective, strong, hard, sound, tough) |
| rugged |
| eternal(adjective, enduring, lasting, permanent, recurrent) |
| vigorous(adjective, strong, sound, tough, solid) |
| changeless(adjective, set, firm, solid, stable) |
| everlasting(adjective, strong, stable, constant, enduring) |
| hale(adjective, strong, sound, tough, solid) |
| immutable(adjective, calm, strong, solid, steady) |