dernier vs. hier

In the lesson 10.0 quiz, question no. 4, the correct answer uses " hier" soir instead of " dernier ' soir. Why? Doesn't dernier mean "last"?

Bonjour HenriTuck! Thanks for your post! Technically, you could say "dernier soir" and you would be understood. But the most common way to say 'last night' or 'last evening' is "hier soir." This is because "hier" means 'yesterday' and together with "soir" you know for sure you are talking about yesterday's evening or night. I hope this has helped clarify. All the best for your French learning! :D Marie Claire