I became aware of what I like to call a "plural of convenience" (POC) after I tried my hand at crossword constructing. I remember an early attempt where I had only one pesky corner remaining to be filled. The solution turned out to be simply a matter of adding an "s" to one of the words in that corner and, kaboom, the grid was complete. This is a big milestone for a fledgling constructor, believe me.
Imagine that you have invested hours on a puzzle and have filled in all of the grid except the last corner. There, one possible solution would work except that a word that fits four out of the five required squares, say FANG, is, unfortunately, a letter short of the number of squares in that slot. And then you see that by simply adding an "S" to FANG, it all falls into place. Woo-hoo!
Who could resist? I couldn't, and it appears other constructors are in the same boat. I've never seen a puzzle that didn't have a POC or two, or sometimes many more, even in top-tier ones like the NYT or LAT.
That first experience got me hooked on POCs, but I still had a tinge of regret that I had to resort to what is essentially a short cut in constructing my puzzle. I had filled up additional grid space without adding anything of substance. FANGS takes up 25% more grid space than FANG, but adds little if any additional value.
I should mention that POC is not a grammatical term. It's a crossword term that means adding an "S", "ES", or dropping a "Y" and adding "IES", (whether the word be a noun or verb*) in order to boost the word's letter count and give it more grid space filling power. POCs make it easier to fill the grid.
Not all POCs are the same. I'm seeing four levels, from the common-as-dirt to the deal-killer.
For more, check out my post, POC levels.
*Often times the word getting an "S" or "ES" can be clued as either a noun or verb. LOVES would be an example. Clueing it as a verb rather than a noun doesn't change the fact that a POC has been used to boost the letter count and---I think it's worth repeating---make it easier to fill the grid. .