The other thing about definitions of horror that bothers me (and this goes for my own definition in BNW), is that I have this inkling that something is being left out. I get the sense, based largely on visits to bookstores and libraries, and to a lesser extent, book reviews, that “horror” is applied to works of fiction that merely partake of the furniture of horror (vampires, ghosts, werewolves, elder gods, the word “eldritch”, etc.), but which are not particularly evocative of the emotion of horror (fear, shock, dread, etc.). And I mean that they are not evocative of these feelings by authorial choice, as opposed to, say, bad writing. For example, the Laurel K. Hamilton “Anita Blake” series of books, which is about a vampire-hunter, and includes all kinds of were-beasts and whatnot, is primarily (at least in the later installments) erotic in nature, and not particularly fear-inducing. But her books are almost invariably shelved in the horror sections of book stores.
Wikipedia’s entry for horror fiction includes this sentence: “Since the 1960s, any work of fiction with a morbid, gruesome, surreal, or exceptionally suspenseful or frightening theme has come to be called ‘horror’.” This could possibly be interpreted as supporting my hypothesis, in that works that are merely “morbid,” “gruesome,” or “surreal” are not necessarily written to induce feelings of horror. But that’s the closest I can come to finding a citation that supports my inkling. Reviews are not especially useful for this sort of defining, since, unless one has actually read the work under review, it’s hard to know which sense the reviewer intends; in the absence of evidence, the standard definition is safest to apply, although, as I said, I’ve seen reviews that give me the impression that the use of “horror” might be broadening. (And unfortunately, I didn’t save any, and don’t even recall what works were under review, so it’s entirely possible that I’m imagining novel uses in my spare time. But I don’t think I am.) Time will tell, I suppose.