| fixed(adjective, secure, severe, harsh, determined) |
| formal(adjective, tough, firm, fixed, distant) |
| hang tough(adjective, tough, sharp, difficult, wild) |
| hanging tough(expression, adjective, firm, determined, usual) |
| hard(adjective, tough, severe, sharp, firm) |
| hard-line(adjective, tough, severe, difficult, stiff) |
| hard as nails(expression, adjective, idiom, tough, firm) |
| hardline |
| headstrong(adjective, hard, tough, sharp, firm) |
| hold the fort(expression, adjective, idiom, tough, firm) |
| hold the line(expression, adjective, idiom, tough, firm) |
| immured(adjective, restrained, captive, confined, enclosed) |
| incompliant(adjective, tough, severe, firm, wild) |
| incurable(adjective, tough, difficult, wild, awkward) |
| indocile(adjective, tough, difficult, wild, awkward) |
| indomitable(adjective, tough, difficult, wild, awkward) |
| inelastic(adjective, tough, severe, firm, harsh) |
| inexorable(adjective, tough, severe, firm, harsh) |
| inflexible(adjective, severe, firm, steady, fixed) |
| insoluble(adjective, tough, difficult, wild, awkward) |