| refractory(adjective, tough, firm, difficult, determined) |
| tenacious(adjective, tough, firm, difficult, resist) |
| uncompromising(adjective, mean, hard, firm, deliberate) |
| intransigent(adjective, tough, determined, resolute, stubborn) |
| recalcitrant(adjective, tough, firm, difficult, awkward) |
| adamantine(adjective, tough, determined, resolute, stubborn) |
| contrary(adjective, tough, difficult, determined, awkward) |
| determined(adjective, tough, firm, deliberate, usual) |
| immovable(adjective, mean, hard, determined, usual) |
| rigid(adjective, mean, hard, tough, firm) |
| unrelenting(adjective, mean, hard, tough, firm) |
| set(adjective, firm, usual, sure, planned) |
| unbending(adjective, mean, hard, tough, determined) |
| wayward(adjective, tough, difficult, awkward, obstinate) |
| bull-headed(adjective, obstinate, stubborn, willful) |
| bullet-headed |
| contumacious(adjective, tough, firm, determined, unreasonable) |
| doctrinaire(adjective, opinionated, dogmatic) |
| dogmatic(adjective, determined, fixed, rigid, strict) |
| hard(adjective, mean, tough, harsh, determined) |