être dur de comprenure

to be slow to understand things

Comprenure is a distinctly Quebec word for the faculty of understanding, built from comprendre the way fermeture is built from fermer. Someone dur de comprenure is thick when it comes to picking things up, though in Quebec the phrase often carries a knowing edge, aimed at someone who is stubbornly refusing to get the point rather than genuinely struggling.

Je lui ai tout réexpliqué trois fois, il est donc dur de comprenure.

I explained it all to him three times over, he really is slow to catch on.

Comprenure goes back to at least 1835. It is just comprendre (to understand) with the suffix -ure tacked on, the same pattern that turns fermer into fermeture, applied here to a word that only really stuck in Quebec and Belgium.

Quebec