| Rating | Solver | Clue |
|---|---|---|
| REINFORCE | Toughen | |
| INURE | Toughen | |
| TEMPER | Toughen (steel) | |
| TOUGHENED | Of Toughen | |
| TOUGHENING | Of Toughen | |
| ENDURE | To harden; to toughen; to make hardy. | |
| ANNEAL | Princess Royal and Pacino join forces to toughen metal | |
| PLANISH | To make smooth or plane, as a metallic surface; to condense, toughen, and polish by light blows with a hammer. | |