Diet vs dietary

Diet is a noun and dietary is an adjective, so there's no answer to your question.

Rover

Hello, Rover!

Thank you very much for your helpful answer. But I asked about the difference because in on-line dictionnaries they give explanations of "dietary" as of a noun, as well :) Here is the link: http://www.onelook.com/?w=dietary&ls=b

The definition of "dietary" as a noun on the OneLook dictionary doesn't make any sense. I advise ignoring them (both the definition and the dictionary) and switching to a better dictionary.

Here are two that seem pretty good:

http://www.learnersdictionary.com/

I find it very strange that many of those online dictionaries give "dietary" as a noun. I have never, ever heard "dietary" used as a noun and I suggest you avoid using it that way, even if it's in some dictionaries.

My experience with 'dietary' is the same. Never heard it as a noun.

CJ

Thank you very much for your help!

I'm surprised myself, because I even looked it up in a printed big thick oxford dictionnary, and even there they give this word as a possible noun but in plural, though (dietaries - restricted food, like that).