| impregnable(adjective, strain, firmness, labour, hardiness) |
| non-fluctuating(adjective, strain, firmness, labour, hardiness) |
| tight(adjective, strain, firmness, labour, hardiness) |
| resolute(adjective, calm, close, strong, secure) |
| devoted(adjective, good, close, strong, kind) |
| non-stop(adjective, continual) |
| unfailing(adjective, good, change, strong, continue) |
| abiding(adjective, calm, strong, secure, tough) |
| determined(adjective, good, strong, flat, firm) |
| habitual(adjective, reasonable, common, ordinary, usual) |
| perennial(adjective, stable, continuous, stability, enduring) |
| persevering(adjective, strong, flat, firm, certain) |
| relentless(adjective, continue, firm, determined, steady) |
| unflagging(adjective, strong, firm, certain, determined) |
| even(adjective, adverb, calm, strong, sound) |
| never-ending(adjective, steady, continuous, endless, infinite) |
| unchangeable(adjective, calm, strong, secure, moderate) |
| unfaltering(adjective, strong, firm, solid, certain) |
| unswerving(adjective, close, strong, correct, firm) |
| frequent(adjective, common, usual, steady, regular) |