One minute on Wikipedia would have disabused you of that wrong notion:
> If the joining of the words or signs is orthographically represented with a hyphen, the result is a hyphenated compound (e.g., must-have, hunter-gatherer). If they are joined without an intervening space, it is a closed compound (e.g., footpath, blackbird). If they are joined with a space (e.g. school bus, high school, lowest common denominator), then the result – at least in English – may be an open compound.
> If the joining of the words or signs is orthographically represented with a hyphen, the result is a hyphenated compound (e.g., must-have, hunter-gatherer). If they are joined without an intervening space, it is a closed compound (e.g., footpath, blackbird). If they are joined with a space (e.g. school bus, high school, lowest common denominator), then the result – at least in English – may be an open compound.
https://en.wikipedia.org/wiki/Compound_(linguistics)