| cruel(adjective, strong, hard, tough, severe) |
| curt(adjective, severe) |
| cussed(adjective, tough, firm, unreasonable, grim) |
| customary(adjective, firm, determined, usual, regular) |
| cutting(adjective, severe) |
| dead set(adjective, determined, resolute, uncompromising, unshakeable) |
| dead set on(expression, adjective, idiom, determined, usual) |
| decided(adjective, firm, determined, usual, regular) |
| decisive(adjective, firm, determined, usual, regular) |
| definite(adjective, firm, determined, usual, unreasonable) |
| demanding(adjective, severe) |
| demure |
| die-hard(adjective, determined, resolute, uncompromising, unshakeable) |
| disciplinary(adjective, strong, hard, tough, severe) |
| disciplined(adjective, severe) |
| disobedient |
| draconian(adjective, severe) |
| dry(adjective, severe) |
| dyed-in-the-wool(adjective, strong, hard, tough, severe) |
| endless(adjective, persistent, constant, pitiless, unyielding) |