"racehorse" vs "racing horse"

[Morphin]

Hey guys!

Can anybody tell me if there's any difference between "a racehorse" and "a racing horse".

I think "race" tells us what kind of the horse, while "racing" is used like an adjective here to say what the general purpose of "horse" is. So which one is more common?

And can I write "a race horse" (as two separate words)? Are there any clear rules for this?

Thank you in advance!

[Mister Micawber]

Can anybody tell me if there's any difference between "a racehorse" and "a racing horse".-- I don't find the latter natural at all.


And can I write "a race horse" (as two separate words)?-- Yes. Are there any clear rules for this?-- The rule is usage. Nine on-line general dictionaries list it as two words, and 19 list it as a single word.
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Native English teacher at Mister Micawber's

[Morphin]

Thank you, Mister Micawber!