Ah... the native speaker arrogance... I corrected a student of mine who consistently referred to health as healthiness. i.e. "You can work there if you have good healthiness" - which just sounds so wrong. She swore she had seen it in a dictionary, I said that was impossible. But I cannot find a site or entry in a dictionary to prove it, in fact, she seems to be right - healthiness is referred to as a synonym to health everywhere I look. Am I crazy? Help!
It sounded funny to me too, but you're right - it's out there.

Your student's usage is off though - it appears you are in a STATE of healthiness, you don't HAVE healthiness.

Or, maybe not. I'm learning new words all the time.
You didn't check deep enough, imantaghavi - it is a simple matter to put [url=http://www.thefreedictionary.com/healthiness ] HEALTHINESS[/url] into the same dictionary's search bar.

People above have been nibbling at it, but it seem to me that 'healthiness' usually refers to the quality of something that produces health in an organism, while 'health' refers to the condition of the organism itself.
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Yep, i came across the word healthiness only today, and was surprised to learn it exists. I'm not a native English speaker by the way. But then I searched and found this sentence:

" I originally set out to compare the relative healthiness of the non-soda beverages at my college's cafeteria"

That helps differentiate the usage / meaning of the two words a bit. Simply put, I think health is, well, your general physical health, and healthiness is more about the idea or the state of being healthy / in good health.

We have Wellness but not healthiness.

Check the following link: http://www.thefreedictionary.com/health

Hope it helps

Students: We have free audio pronunciation exercises.
 Mister Micawber's reply was promoted to an answer.

Yes. You're right.