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What is appropriate usage of "numerator", "denominator", and "nominator" to refer to parts of a fraction?

I'm posting this question and answer here because I had little luck finding a clear answer through Google. I realize that it's not really mathematics, but I think it's worth mentioning as an educational issue.

Ideally, the question at English.stackexchange would address this completely, however they have closed it with the reason: "you can just look it up". I agree that this is possible, but I don't think that reveals the consensus. I wanted to allow for more opinions to be expressed. (Below, I argue that "nominator" should be discouraged.)

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I this is triggered by a recent comment of mine I apologize for causing this. It is in fact easy to look up these terms (e.g. at, which supports your position. I have no problem whatsoever with using numerator and do admit that using nominator was the result of a moment of thoghtlessnes of a non native speaker. – user20266 Jun 16 '12 at 14:44
Hi @Thomas No no, this post was not wholly caused by you :) You are actually the third incident that I have run across this recently, and so I started searching previous posts and I figured we could use a post to refer to on the topic. Please don't feel picked on: rather feel that you inspired me to action! I did not intend to make you feel like a troublemaker :) – rschwieb Jun 16 '12 at 14:46
I see, now I'm 'an incident'! ;-) Thanks for the clarification – user20266 Jun 16 '12 at 14:48
Henceforth, this shall be known as "the @Thomas incident"! – The Chaz 2.0 Jun 16 '12 at 14:54
@TheChaz I saw this coming, kind of, thank you! rschwieb: are you implying, then, that the remaining 1% of these 'incidents' are to be considered mischievous, and this even by intention? What a gruesome observation! – user20266 Jun 16 '12 at 15:07
up vote 10 down vote accepted

The numerator is the top part of a fraction, the denominator is the bottom part, and nominator is not an appropriate term for any part of a fraction.

I have seen nominator used to mean both "numerator" and "denominator". According to a question on this at English.stackexchange, this use of "nominator" is exceedingly rare.

Rather than people having been taught that "nominator" was appropriate, I think that it is far more often the case that the use of "nominator" is an eggcorn that has arisen due to its resemblance to the other two words.

I think using "nominator" should be discouraged because it already has a wholly different meaning, and has no etymological connection to fractions to speak of. It is also helps to confuse the meanings of the proper terms, if it is mixed with them.

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It would be amusing, for fractions such as $1/(a/b)$, to call $a$ the nominator and $b$ the denumerator. Admittedly, this twisted symmetry with normal usage is perverse, but I am currently grading exams and so feel entitled to a bit of perversity. – Harald Hanche-Olsen Jun 16 '12 at 14:37
@HaraldHanche-Olsen Those of us grading deserve all the comfort we can get! – rschwieb Jun 16 '12 at 14:40

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