| ruthless(adjective, hard, rough, harsh, cruel) |
| standing pat(adjective, determined, resolute, obstinate, uncompromising) |
| staunch(adjective, clear, strong, tough, severe) |
| strong-willed(adjective, determined, resolute, uncompromising, unshakeable) |
| callous(adjective, hard, tough, rough, harsh) |
| cruel(adjective, strong, hard, tough, severe) |
| flinty(adjective, close, strong, hard, tough) |
| hardheaded(adjective, strong, hard, tough, determined) |
| hidebound(adjective, close, severe, firm, determined) |
| indurate(adjective, mean, hard, firm, determined) |
| inhuman(adjective, harsh, cruel, determined, fierce) |
| merciless(adjective, hard, rough, harsh, cruel) |
| persistent(adjective, strong, tough, severe, flat) |
| pertinacious(adjective, tough, determined, resolute, obstinate) |
| pigheaded(adjective, mean, hard, tough, determined) |
| precise(adjective, correct, severe, certain, limited) |
| refractory(adjective, hard, tough, rough, firm) |
| stony(adjective, hard, firm, solid, careless) |
| tenacious(adjective, clear, strong, tough, severe) |
| undeviating(adjective, strong, flat, harsh, certain) |