English word nonexistent comes from English existent, English non-

Detailed word origin of nonexistent

Dictionary entry	Language	Definition
existent	English (eng)	Existing; having life or being, current; occurring now (archaic) a being or entity that exists independently.
non-	English (eng)	Used in the sense of not, to negate the meaning of the word to which it is prefixed.
nonexistent	English (eng)	Not existent; not real.

Words with the same origin as nonexistent