The same phenomenon occurs when more than one forum is brought to the table - which possibly makes it two phenomena.
The issue at stake here is the treacherous problem of Latin plurals, an area that holds the possibility for the most dreadful faux pas in polite society.
A Dunedin city councillor sailed his linguistic ship through those stormy waters recently, when he confidently discussed the council's various fora during a debate at the municipal chambers to decide whether to change the way they are run.
He did that despite afterwards telling the Otago Daily Times he suffered no Latin classes during his school years.
The problem with fora, if you believe the Oxford dictionary, is it appears to have a narrower meaning than its singular form.
While forum is listed as a medium where ideas and views on an issue can be exchanged, fora is listed as the plural of forum, a public square in an ancient Roman city used for judicial and other business.
This is unlikely - unless togas make a return - to be an issue at the Dunedin municipal chambers.
Which brings us to my central point.
Them Latins were quite excellent at dealing with their own plural forms, but try to dump them on an unsuspecting English-speaking populace and things get difficult.
And there seems little rhyme or reason some Latin words retain their plurals and some take their English equivalent.
Virus is Latin but takes an es, while for radius, either radiuses or radii are apparently acceptable.
Which is why stadiums and forums are all right by me.
My favourite so-called Latin plural relates to more than one cephalopod mollusc - or two "octopi" - precisely because it isn't Latin.
In an attempt to get those confusing foreign plurals right, many mistake the word octopus as having a Latin ancestry, and chuck a Latin plural on the end.
In fact, the word is Greek, and if you were desperate to impress your new girlfriend's academic parents, octopodes would be the way to tackle more than one.
But remarkably for our language, the more simple English es plural form is the standard.
And that is no doubt a relief to many octopuses.
