nonexistent, non-existent or non existent? [duplicate]

I see various spellings of the same, which one is correct?

I have considered that the spelling might differ if it is British or American English, but as English isn't my native speak I have no clue.

For AmE, you should go to the best N. American dictionary, and use the version there:

nonexistent

adjective

\"+\

: not having existence

Merriam-Webster Unabridged Dictionary

At COCA
CORPUS OF CONTEMPORARY AMERICAN ENGLISH

NONEXISTENT 1727

NON-EXISTENT 443

thus there's a heavy use of both, but I'd follow the M-W U.

BrE: Non-existent used to be British spelling, but a couple of years back they did away with the hyphens of 16,000 hyphenated words.

AmE: the answer above is the valid answer, just one word: nonexistent The American Heritage Dictionary 5th Ed. confirms this.

So it appears the Standard Usage in both side of the Atlantic is one unhyphenated word.