Phoenix
anthrax
Pheonix
travaux
Five letter words starting with C and ending with X are calyx and codex.
Flax.
cortex
Examples of common nouns ending in X:axboxcrucifixcruxduplexequinoxflaxfoxhexibexindexjinxlarynxloxlynxmatrixminxmixonyxoryxoxparadoxphoenixphloxpoxprefixrouxsexsixsmallpoxspandexsuffixsyntaxtaxthoraxvortexwax
A four letter word beginning with C and ending with X is crux.
box, fox, ibex
Phoenix
phoenix?
orthodox