Adjectives ending with the letter X are listed in this post.
before-tax, biconvex, bordeaux
circumflex, complex, concavo-convex, contraplex, convex, convexo-convex
decomplex, devex, diplex, duplex
faux, fix, flux
perplex, plano-convex, pretax, pre-tax, prolix, property-tax, pseudodox
Hope this word list had the adjective that ends in X you were looking for. Additional descriptive words can be found in the other pages on this site.