This is the 879th most frequent French word.
aucun
"None" or "no" (depending on context).
'Aucun' is used here as an adjective modifying 'livre', indicating the absence of any books.
Je n'ai aucun livre à lire.
I have no books to read.
'Aucun' is used here as a pronoun referring to none of the group of friends.
Aucun de mes amis n'est disponible aujourd'hui.
None of my friends are available today.
'Aucun' emphasizes the absence of any problem, negating the presence of problems.