| persistent(adjective, tough, firm, unreasonable, grim) |
| pertinacious |
| perverse(adjective, tough, firm, cruel, unreasonable) |
| rabid(adjective, harsh, violent, cruel, vicious) |
| raging(adjective, harsh, violent, cruel, vicious) |
| recusant |
| regretless |
| resolute(adjective, determined, uncompromising, unshakeable) |
| resolved(adjective, determined, resolute, uncompromising, unshakeable) |
| rock-ribbed(adjective, determined, resolute, uncompromising, unshakeable) |
| rough |
| rude |
| satanic(adjective, mean, hard, harsh, cold) |
| sorrowless |
| soulless(adjective, mean, hard, harsh, cold) |
| steady(adjective, persistent, constant, pitiless, unyielding) |
| stern(adjective, mean, severe, harsh, cruel) |
| stiff(adjective, harsh, cruel, determined, fierce) |
| stony(adjective, mean, hard, severe, harsh) |
| stop at nothing(expression, adjective, idiom, harsh, cruel) |