Expanding your vocabulary to include terms that describe your character, a chapter, book, scene, or genre opens up the door for new ideas to come flowing in. You may never use any of them, but they inspire you to write with that defined tone. I decided to search "horror vocabulary" to see what comes up and defined horror with a few words of my own also. Here is a link to some horror vocabulary words:
Vocabulary list #1
Vocabulary list #2
Notice how there are always contrasting tones to the one that you choose. In a horror book there will be "scary words", and there will be words that make you calm; and unprepared for what is to come. In a romance there will be words of love and words of conflict. We already know this as writers, but it put me in a writing mood!