Ask someone to name a word that starts with "x", and you'll likely get “xylophone” or “x-ray.” Not very inspiring, right? What if you asked someone to name an adjective that starts with "x"? Several blank stares await you. Adjectives that start with "x" do exist, though. For the most part, they fall into one of four categories (xanth, xen, xer, or xyl) based on their Greek roots.