| uncompromising(adjective, tough, firm, difficult, rigid) |
| inflexible(adjective, strong, hard, tough, severe) |
| rigid(adjective, strong, hard, tough, severe) |
| stern(adjective, hard, tough, severe, rough) |
| unyielding(adjective, strong, hard, tough, severe) |
| hardline |
| strict(adjective, strong, hard, tough, severe) |
| inexorable(adjective, strong, hard, tough, firm) |
| tough(adjective, strong, hard, rough, firm) |
| adamant(adjective, strong, hard, tough, rough) |
| firm(adjective, strong, hard, tough, severe) |
| hard-shell(adjective, strong, hard, tough, serious) |
| hard-shelled(adjective, hard, tough, severe, rough) |
| indomitable(adjective, strong, hard, tough, difficult) |
| intractable(adjective, tough, firm, difficult, persistent) |
| relentless(adjective, strong, hard, tough, firm) |
| severe(adjective, strong, hard, tough, rough) |
| steadfast(adjective, firm, persistent, obstinate, insistent) |
| cantankerous(difficult, awkward, persistent, obstinate, stubborn) |
| contrary(difficult, awkward, persistent, obstinate, stubborn) |