What if a student in a class asks!

@helenS and what does arius mean? and how did it come to Latin ?

@in10RjFox "–arius" was used to form adjectives from nouns or numerals.
Examples:
ordō (“line, row”) + -ārius → ordinārius (“ordinary”).
quaternī (“four at a time, by fours”) + -ārius → quaternārius (“quaternary”).

It came from earlier "-āsio-", which, by an ordinary (hah!) rhotacism became "-ario".

@helenS I am now curious why arius was chosen to make adjectives. ? Any basis. For I see it as 100 lies to cover up one lie.

And is linguistics your major?

Rhotacism is difficulty in pronouncing the. R. How will it cause bringing in the R ?

@in10RjFox I studied physics, not linguistics, but I'm interested in linguistic phenomena.
Rhotacism refers to the substitution of "s" by "r" between two vowels.
English example: "was" → were
–arius was never "chosen" to make adjectives. It's language, it's not a result of conscious decisions.

@helenS
So the entire thing can be just our deduction based on assumptions or post mortem logical reasoning?

@in10RjFox ... informed assumptions.

@helenS and who was the informer? and who made the assumption? Was there any documented evidence to say this was how the word was derived ?

Similarly, is there any documentation for why "H" is silent in the word "Honest".