relax
remex
remix
fedex
addax
admix
affix
annex
inbox
codex
latex
infix
Five letter words starting with C and ending with X are calyx and codex.
Flax.
cortex
A four letter word beginning with C and ending with X is crux.
Extra
Extra is a five letter word for surplus. E X T R A.
phoenix?
Five letter words with second letter x are:excelexertextraaxiomexpel
epoxy
Pheonix
The word faux has a silent x, pronounced [foh].
epoxy, prexy