X-Ray - In a horror movie, X-Rays will also discover that you have something nasty growing inside of you, or a metal device implanted by aliens. They can also be used to find things stuck up your bum.
XXX - Porn in a horror movie will corrupt you into a seedy world of isolation and depravity. Masterbating on TV is banned anyway so what's the point?
X-Factor - God this shower fits into the horror genre, don't you think?
Xtreme - Anyone that spells the word like this is not.
Xenomorph - This little beauty will eat you eyeballs with its 'little mouth'. Tasty!