The answer is still the same as it was in 2009,
Thridding
http://www.yorkshireridings.org/news/the-yorkshire-ridings.html
How about triven or treeven? And numbers not evenly divisible by 3 are trodd.
It sounds as if many people are making up words for this. At best, they’re referencing words that someone else has made up, with the age of the word lending credibility.
I would suggest something like “trifactor” implying three is a factor. In this system, even numbers are “bifactor”, divisible by 4 might be “quadfactor”, or maybe “tetrafactor”
The good folk of Yorkshire, all 5.3 million might be surprised to find that the word ‘riding’ and its antecedent ‘thridding’ were made up, given that we’ve lived here for a around a thousand years give or take a decade or two.
There are exceptions, yes. However, I think that unless a word is widely (geographically) known, it’s history of use (or lack of) isn’t as relevant. Surely 5.3 million is a large number, but if a [different] word had fallen entirely out of use, raising it from death isn’t any better than inventing a new word.
I think you will find the use of the word riding is in very wide use, look in any atlas
“Riding” comes from a noun meaning “third part”. It never meant, and does not now mean, “divisible by three”.
…and is derived from ‘thridding’, which is something divisible by three, as I posted a few years ago in this thread, or rather its that act of dividing into three
“Something divisible by three” or “the act of dividing into three” do not mean the same thing as “divisible by three”. Nouns are not adjectives.