grammatical number - Word for nouns with multiple plural forms

Some nouns have multiple plurals, this article from Merriam Webster names a few. I'm wondering if there is a word to describe this, a word meaning having multiple plural forms. To put it in a sentence (two sentences to allow noun and adjective answers):

1. Syllabus is a(n) (insert word), because it has two plural forms.




2. Syllabus is (insert word), because it has two plural forms.

I have scanned through the Wikipedia page on English plurals which has a lot of terms for different plural forms, however, I have not come across a term for words with multiple plural forms. I've also scanned through some blogs on the Oxford Dictionaries website, but to no avail.

Some of the examples from the aforementioned Merriam Webster article:

One referendum, multiple referendums or referenda 1

One syllabus, multiple syllabuses or syllabi 1

One gymnasium, multiple gymnasiums or gymnasia 1

One referendum, multiple referendums or referenda 1

One miasma, multiple miasmas, miasmata or miasms 1

One terminal, multiple terminuses or termini 1

Answer

From A University Grammar of English
By Randolph Quirk.

Foreign plurals (Nouns) often occur along with regular plurals (nouns). They are commoner in technical usage, whereas the -s plural is more natural in everyday language; thus formulas(general)~formulae (in mathematics), antennas (general and in electronics) ~ antennae (in biology).

Foreign plural nouns often make their plural according to the orthography of the language they were taken from (e.g. Latin or Greek or Italian etc.,).

For a given word, sometimes foreign plural and regular plural nouns have different meanings e.g. medium has two plurals: mediums/media, both plural forms have different meanings.

There is a exhaustive explanation in Lesson XVIII of A Comprehensive Grammar of the English Language By George Payn Quackenbos.

So, whenever there is more than one plural form of the given noun, then you can individually refer them as foreign plural and/or regular plural according to their orthography.