| permanent(adjective, strain, firmness, labour, hardiness) |
| steady(adjective, strain, firmness, safe, labour) |
| viable(adjective, strain, firmness, labour, hardiness) |
| impenetrable(adjective, unyielding, safety) |
| secure(adjective, sound, reasonable, firm, true) |
| unassailable(adjective, strong, secure, resolute, safe) |
| invincible(adjective, strength, do, win, unyielding) |
| invulnerable(adjective, strong, secure, resolute, safe) |
| inviolable(adjective, secure, safe, snug, intact) |
| unconquerable(adjective, strength, do, win, insurmountable) |
| indomitable(adjective, strength, do, win, steadfast) |
| inexpugnable(adjective, safety) |
| safe(adjective, secure, harm, unquestionable, snug) |
| insuperable |
| unattackable(adjective, safety) |
| all-conquering |
| indestructible(adjective, unyielding) |
| protected(adjective, secure, safe, snug, intact) |
| solid(adjective, safe, unyielding, sheltered, protected) |
| unbeatable |