The use of the optimum formula of x compounds is relatively small.

What is the opposite of the word optimum? Is it non-optimum? Could inefficient be a choice?

  • Optimum is generally equivalent to "best" or "best fit", but not necessarily "most efficient" - there's other ways of being the best (e.g. "optimum strength"). You would need to say optimally efficient for inefficient to really be the opposite.
    – LawrenceC
    Dec 21, 2015 at 14:07

4 Answers 4


It depends on what you mean by opposite:

  1. Do you mean exact opposite, as the hottest one -- the coldest one?
  2. Or do you mean just negation, like the hottest one -- not the hottest one?

For exact opposite

I can't find antonym for the adjective optimum/optimal here.
Although antonym for the noun optimum is the noun pessimum, the word pessimum neither can be used as adjective, nor has correspondent adjective in English (and you certainly need an adjective here).

For negation

The synonym for non-optimal is suboptimal.

The use of the optimum formula of x compounds is relatively small.
On the contrary, suboptimal formulas/suboptimal formulae are widely used.

Post scriptum

I recommend you changing the word optimum to optimal here, as you certainly need an adjective (although the word optimum can be used as adjective too, most people prefer to interpret it as noun). And together with some other changes:

The use of the optimal formula for x compounds is relatively rare.
On the contrary, suboptimal formulas/formulae for x compounds are widely used.

(If I understood your original sentence correctly.)


There's something wrong with your sample sentence. I know because I have no idea what it means.

Apart from that, I prefer "optimal," which is a natural adjective, to "optimum," which is not.

That said, there is no exact antonym for "optimal." But, since it means "the best possible under the circumstances," you might as well make do with "worst possible," "least efficient," or simply "horrid."


From the Latin, pessimum, but that word didn't actually make it into English. Instead there's optimism and pessimism, but those are entirely different.

Because the word didn't cross languages with its native opposite, though, it doesn't have a clear one in English. Ricky has some decent ones.


'optimum' is not a native English word. 'optimal' would be one. As such, its antonym will be 'non-optimal'(used frequently in mathematics).

'optimum' is an example of mixed English, which is usually spoken by non-native speakers. I, being an Indian, have seen examples of this among locals.

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