| fixed(tough, severe, firm, stiff, inflexible) |
| flintlike(adjective, tenacious) |
| flinty(adjective, strong, hard, tough, severe) |
| foolhardy(determined, impulsive, stubborn, reckless, impetuous) |
| forbidding(adjective, strong, hard, tough, severe) |
| frowning(adjective, strong, hard, tough, severe) |
| gluey |
| glutinous |
| gummy |
| hang-tough(adjective, strong, hard, tough, severe) |
| hard-boiled(adjective, strong, hard, tough, severe) |
| hard-core(adjective, strong, hard, tough, severe) |
| hard-headed |
| hard-line(adjective, strong, hard, tough, severe) |
| hard-shell(adjective, strong, hard, tough, severe) |
| hardened(adjective, determined, resolute, uncompromising, unshakeable) |
| harsh(adjective, strong, hard, tough, severe) |
| heedless(determined, impulsive, stubborn, reckless, impetuous) |
| imprudent(determined, impulsive, stubborn, reckless, impetuous) |
| incompliant(adjective, stubborn) |