hard, difficult
Je sais, ça paraît terriblement ardu, mais croyez-moi, on va y arriver.
I know it seems terribly difficult, but believe me, we’ll get there.
— Le Scaphandre et le Papillon (2007)
Ou bien très ardu.
Or else very arduous.
— La Plateforme (2019)
L'anglais technique de ce manuel est assez ardu.
The technical English in this manual is quite difficult.
Ça a été un combat ardu.
It was an uphill battle.