| intransigent(adjective, resist, determined, resolute, obstinate) |
| inexorable(adjective, strong, hard, tough, resist) |
| inflexible(adjective, strong, hard, tough, firm) |
| unrelenting(adjective, strong, hard, tough, resist) |
| adamant(adjective, strong, hard, tough, firm) |
| stubborn(adjective, characteristic, quality, strong, hard) |
| unyielding(adjective, strong, hard, tough, firm) |
| tough(adjective, strong, hard, firm, unreasonable) |
| flinty(adjective, strong, hard, tough, firm) |
| obdurate(adjective, strong, hard, tough, resist) |
| rigid(adjective, strong, hard, tough, severe) |
| uncompromising(adjective, tough, resist, determined, resolute) |
| unbending(adjective, strong, hard, tough, resist) |
| unbreakable(adjective, strong, tough, severe, firm) |
| relentless(adjective, strong, hard, tough, resist) |
| hard(adjective, strong, strength, tough, firm) |
| impenetrable(adjective, set, tough, firm, stiff) |
| firm(adjective, strong, hard, tough, determined) |
| indestructible(adjective, firm, rigid, unyielding, steely) |
| rock-hard(adjective, firm, rigid, unyielding, steely) |