Adjectives ending with the letter X are listed in this post.
after-tax, anti-tax
before-tax, biconvex, bordeaux
circumflex, complex, concavo-convex, contraplex, convex, convexo-convex
decomplex, devex, diplex, duplex
faux, fix, flux
heterodox
implex, incomplex
lax, leptothrix
manx, multiplex
oeil-de-perdrix, orthodox
perplex, plano-convex, pretax, pre-tax, prolix, property-tax, pseudodox
quadruplex
reflex, relax
six
triplex
ultra-orthodox, unorthodox
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.
Please add more adjectives to make this list more complete: