| adamant(strong, hard, tough, sturdy, rigid) |
| adamantine(strong, hard, tough, sturdy, rigid) |
| astringent(strong, hard, tough, sturdy, rugged) |
| austere(strong, hard, tough, sturdy, rugged) |
| authoritarian(strong, hard, tough, sturdy, rugged) |
| bitter(strong, hard, tough, sturdy, rugged) |
| bullheaded(strong, hard, tough, sturdy, rugged) |
| by the book(expression, idiom, strong, hard, tough) |
| dense(strong, hard, tough, sturdy, rigid) |
| determined(strong, hard, tough) |
| disciplinary(strong, hard, tough, sturdy, rugged) |
| dyed-in-the-wool(strong, hard, tough, sturdy, rugged) |
| ferric(strong, hard, tough, sturdy, rigid) |
| ferrous(strong, hard, tough, sturdy, rigid) |
| firm(strong, hard, tough, sturdy, rigid) |
| flinty(strong, hard, tough, sturdy, rugged) |
| forbidding(strong, hard, tough, sturdy, rugged) |
| frowning(strong, hard, tough, sturdy, rugged) |
| grim(strong, hard, tough, sturdy, rugged) |
| hang-tough(strong, hard, tough, sturdy, rugged) |