He writes with an iron pen. [That which he writes will not be easily altered.]
More Latin Proverbs:
What I do against my will cannot be said to be my own act.Latin
They give, to find a pretext for asking.
Latin
Colewort twice cooked.
Latin
Colewort twice cooked.
Latin
Submit to the rule you have yourself laid down.
Latin
Presumption first blinds a man, and then sets him a running.
Latin