# Where to place the plural mark in 3-word compound words?

This question is similar to this one (and other on the site), but with three elements in the compound word. In a technical context, where a bin is a range of frequency values and a bin is referred to by its middle frequency, I would like to refer to frequencies corresponding to bin centers.

➞ My question boils down to: What is the plural of bin center frequency?

From the answer to the linked question, it could be the bins center frequencies as there are multiple bins which have each a single center frequency. but the answer is focused on two-word compounds, so I'm not sure it applies.

On the other hand occurrences on Google are respectively 1,000+ for bin center frequencies and 80+ for bins center frequencies. To me bin center frequencies refers more to the several frequencies of the center of a single bin. I also found the form the bin centers to denote the centers alone, so maybe I could also use the bin centers frequencies, but I feel the bin-centers frequencies would be more correct in this case.

I'm really perplexed. Could you please tell me what is the most correct sentence, and if different, what would be the most usual form in a technical writing?

• A quick Wiki search answers the question. A bin-centres test signal is one which has been constructed such that it has frequency components at FFT bin-centre frequencies. There is very little information on this. To me it sounds like the structure should be a possessive. This may be a question for dsp.stackexchange.com Commented Nov 3, 2022 at 12:35

## 1 Answer

There is a logical way to determine where the plural should go, but you need to be aware that it is not always followed.

In your example it should be 'frequency' that is plural, because 'bin centre' is just modifying 'frequency'.

If you said 'bins centre frequency' it would imply that all the bins have the same centre frequency.

However, this logic is not always followed.

Take the case of 'mother in law'.

'Mother' is the noun, and so should be pluralised, but a great many people (possibly the majority), say 'mother in laws'. It depends if the speaker/writer considers the the phrase to be a compound noun, or a noun with adjective.

• "motherS in law" is the correct plural, Just because many other people use it incorrectly shouldn't be a reason why everyone else should follow suit. ¶ But +1 for giving the generalization that one of the words is always the primary essential word while the secondary words modify or restrict it. Commented Nov 3, 2022 at 13:21
• @RayButterworth I completely agree, but I thought I should mention the fact that so many people get it wrong, as it might confuse learners if they are given the correct logic but here a lot of native speakers using 'colloquial' versions in certain cases. Commented Nov 3, 2022 at 13:26
• @PRL75 I haven't seen mother-in-laws as often as I've seen other incorrect plurals like Attorney Generals that arise because people don't realize that the second word is not a noun. Commented Nov 3, 2022 at 17:53
• @AndrewRay LOL, yes. Corrected version: Indeed. "Court Martials" is another that is seen far too often. Commented Nov 3, 2022 at 18:30