approx
bijoux
bollix
cervix
climax
coccyx
convex
cortex
cowpox
duplex
earwax
hatbox
hotbox
icebox
influx
larynx
lummox
matrix
meninx
outbox
outfox
pickax
prefix
premix
prolix
reflex
reflux
smilax
spadix
sphinx
suffix
surtax
syntax
thorax
unisex
vertex
vortex
cortex
Flax.
A four letter word beginning with C and ending with X is crux.
Five letter words starting with C and ending with X are calyx and codex.
djebel
phoenix?
Pheonix
The word faux has a silent x, pronounced [foh].
Texter
travaux
Try flux or flax; latter is healthier.
Calyx, codex and cylix are 5 letter words. They begin with c and end with x.