Is "testes" an inflectional reduplication?

Question

I was supposed to ask this question 1 year ago and it is based on a discussion in this question that I answered: What is a word called that consists of a repetition of one word?

I gave testes as an example of a full reduplication and a commentator told me that "testes is not reduplicated, but rather the plural form of testis".

I know that it is a plural form and it is chiefly in plural form but I thought we can consider testes both a plural form and a reduplication. It is not created by reduplication process but a pattern is reduplicated when you use the plural form. He also noted that testis, testes follows a specific Latin declension in which singular -is is replaced with plural -es. Some other nouns belonging to the same declension: axis, axes; thesis, theses; oasis, oases.

Wikipedia definition of reduplication:

Reduplication in linguistics is a morphological process in which the root or stem of a word (or part of it) or even the whole word is repeated exactly or with a slight change.

The definition says that the repeated part can even be part of the root or stem of a word. I know that the word testes is not created with the usual reduplication process but there is also a form called inflectional reduplication:

A still stricter definition of reduplication would only include inflectional reduplication, i.e., only a reduplication which serves a clear-cut grammatical function, is to be considered an 'actual' form of reduplication, thereby excluding lexical reduplicate forms. Inflectional reduplication, is however probably the most uncommon of all forms of reduplication. Inflectional reduplication is manifested either as a full reduplication or as a partial reduplication, i.e., the copying of only a part of the base.

_{Source: http://reduplication.uni-graz.at/texte/Other_Red_Phen.pdf}

Can someone please shed light on this?

_{Note: Testes is also one of the plural forms of test meaning "The cupel used in treating gold or silver alloys or ore; now esp. the cupel, with the iron frame or basket which contains it, forming the movable hearth of a reverberatory furnace" [OED]}

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Another controversial word is tartar.

For the proper noun Tartar (meaning "a native inhabitant of the region of central Asia extending eastward from the Caspian Sea, and formerly known as Independent and Chinese Tartary." OED), the book "Journal of the Royal Asiatic Society of Great Britain and Ireland" has the following:

Answer 1

I think the key point is that Wikipedia refers to reduplication as a process, not a relationship. That testes starts and ends with the same three letters is a fact. But historically, this fact does not derive from any kind of process of repetition. Otherwise, we'd get thesis, thethe and so on.

You seem to already realize that "tes" is not the actual stem of the word, but you try to get around this by appealing to the idea of partial reduplication. By this logic, you would have to include even more ridiculous examples: any suffixed word that happens to include the sounds of the suffix in the stem. For example: singing, prizes, flitted.

(And lastly, the repetition here merely applies to the spelling, as Edwin Ashworth notes.)

Answer 2

The Italian Wikipedia article has some more examples on reduplication in Latin and they are not quite similar to what happens in testes: https://it.wikipedia.org/wiki/Reduplicazione#Lingue_con_reduplicazione

The key, in my opinion, is that the speaker doesn't perceive a repetition at all in testes. We should check further sources, but as an Italian speaker I pronounce the first e more open than the second: /'tɛstes/ (https://it.wikipedia.org/wiki/Lingua_italiana#Vocali) which in Latin might have been /'testeːs/ (https://it.wikipedia.org/wiki/Lingua_latina#Vocali).

Of course there are differing opinions on how Latin was pronounced, but here we really have no element at all to support the idea of a reduplication.