| perpetual(adjective, determined, steady, persistent, constant) |
| savage(adjective, animal, mean, hard, tough) |
| unswayable(adjective, determined, resolute, rigid, obstinate) |
| austere(adjective, appearance, strong, hard, tough) |
| brassbound(adjective, resist, determined, resolute, persistent) |
| die-hard(adjective, resist, determined, resolute, persistent) |
| hanging tough(expression, adjective, mean, hard, determined) |
| headstrong(adjective, strong, tough, firm, cold) |
| incessant(adjective, firm, determined, steady, persistent) |
| inhuman(adjective, animal, mean, hard, tough) |
| lasting(adjective, certain, persistent, constant, reliable) |
| persevering(adjective, perseverance) |
| pigheaded(adjective, mean, hard, tough, firm) |
| rough(adjective, strong, hard, tough, severe) |
| standing pat(adjective, determined, resolute, obstinate, uncompromising) |
| unflagging(adjective, persistent, perseverance) |
| unshakeable(adjective, determined, resolute, uncompromising) |
| unswerving(adjective, determined, resolute, perseverance, uncompromising) |
| hardened(adjective, hard, tough, harsh, determined) |
| intractable(adjective, appearance, strong, tough, firm) |