I've been reading a book out of a series entitled La Passe-Miroir, which throws me off. Miroir is masculine...it's le miroir. Unless I've misunderstood, the author seems to have constructed a compound word with a meaning along the lines of "The Travel-Mirror" or "The Passage-Mirror" depending on how you wish to translate it.
But why isn't it Le Passe-Miroir ? Surely miroir is the "dominant" noun here, the one being modified. Although passe is feminine, I would have thought the final noun took precedence, resulting in Le Passe-Miroir.
Why is it feminine?