Too many to list: [http://onelook.com/?w=%3F%3F%3F%3F%3F%3Fx&ls=a try this link]
paradox
7 letter word 3rd letter x
7 letter word 3rd letter x
Five letter words starting with C and ending with X are calyx and codex.
Phoenix
phoenix?
orthodox
anthrax
box, fox, ibex
The word faux has a silent x, pronounced [foh].
fox vox box pox
Xeroxes
Lunchbox, ox, fox, lox. helix.