Need an antonym

I’ve checked and went through my big thesaurus but I really haven’t found any antonyms that fit what I’m looking for.
The word is “ideal” and I’m looking for an antonym for it that doesn’t mean “actual”. I’m thinking of “ideal” in the sense of “zenith” and the antonym meaning “nadir”, the worst possible concept.

Practical? Down-to-Earth?

Hrm, no like “ideal” is the best. What would be the worst.

Can you give us the sentence? That might help.

Worst. What’s wrong with the word “worst”? Seems to me that you answered your own question.

You’re not going to get a direct antonym in the sense that you want, because ideal’s opposite is the actual or the concrete. The notion that the ideal is the superlative or best is an associatiated meaning, not a direct one.

You have already noted nadir.
You might use a phrase including antithertical or refer to something as the epitome of evil/stupidity/badness/whatever.

Depending on your context, you might try delusion or illusion (in the sense of a misleading ideal.

Perhaps “dystopian” is what you’re looking for, meaning the opposite of utopian or idyllic.

And if you’re going to follow Tom’s suggestion, it’s spelled “antithetical.” However I’ve always known that word to mean “inimical” more than “nadir”.

I go with con template. Where ‘ideal’ means ‘best’ (as opposed to non-real) then the antonym is ‘worst’.