'Hoole' is a word that is essential to the series and wouldn't have such a good name without it. For wolves, it simply means an owl, but often used to describe the spirit of an owl that guided wolves to the Beyond; and for owls, it is the name of the very important king at least a thousand years ago, King Hoole. 

Hoole is featured on the cover of the tenth book, seemingly unaware that there is a hagsfiend above him!