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I came across the word nocuous. It seems that this word is rarely used (and even the spell-checking of my browser does mark it as a mistake). Noxious, in comparison, is used way more often.

Interestingly, the opposite statement can be applied to their antonyms innocuous and innoxious. Now the comparison between both shows a clear tendency to the use of innocuous (and my browser's spell-checking marks the latter).

The question is, in which contexts should I have a preference to nocuous/innocuous and when should I go with noxious/innoxious? Or are possibly only innocuous and noxious in practical use, while the others are rather formal? Perhaps, innocuous is the well-established opposite to noxious in colloquial?

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What do you mean by "even ELU does mark it as a mistake"? –  Jim May 25 '12 at 20:50
@Jim The spelling check of this page here (ELU) underlines them red. –  Em1 May 25 '12 at 20:52
That's your browser, not the website. EL&U has no spell-checking. –  Jim May 25 '12 at 20:54
@Jim Good to know. Thanks. –  Em1 May 25 '12 at 21:02
@Jim: I think you mean 'ELU has no computerised spell-checking'. –  TimLymington May 25 '12 at 22:40

2 Answers 2

up vote 3 down vote accepted

Innoxious is used in medical, chemical, and certain manufacturing fields to mean that a substance is not injurious, hurtful, or damaging, especially to tissues. Do a Google search for "innoxious medical" and you get 768,000 results. Of course innoxious is the antonym of noxious and a synonym for innocuous. (Those three words appear in Dorland's Illustrated Medical Dictionary, 30th Ed. Nocuous, however, did not merit an entry.) Both Dorland's and Saunders Comprehensive Veterinary Dictionary include in their definitions of noxious the word "pernicious," which in medical dictionaries is defined as "tending to a fatal tissue." That is, something that is noxious can be very damaging to tissues, irreparably so.

So to answer your question, the most commonly used words (as you suspected) are innocuous and noxious. Innoxious has use in certain fields. Nocuous is just not used.

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Shouldn't tissue be issue? (I don't have medical dictionaries on hand.) –  TimLymington May 27 '12 at 15:34
@TimLymington, No. Tissue is correct. It kills the tissue. –  JLG Jun 1 '12 at 15:03
Interestingly, in some non-medical dictionaries, ‘innoxious’ is not found at all, while ‘nocuous’ is found, though marked as literary or formal. –  Janus Bahs Jacquet Aug 26 '13 at 14:17

An interesting question: I didn't know that there were such words as nocuous and innoxious. I'd suggest the answer would be that very few people have heard of these words, and therefore noxious and innocuous would be preferable.

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I think using either, however in-nocently, would be ob-noxious. –  TimLymington May 25 '12 at 22:04

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