uzaludno

1. in vain; futilely
   Uzaludno smo ga čekali ceo sat. — We waited for him in vain for a whole hour.
   Uzaludno je objašnjavati mu, ne sluša. — It's pointless explaining to him, he won't listen.

In speech uzalud is more common; uzaludno is often used in the construction uzaludno je + infinitive.