Linguistic Musings on Twinship

We were invited to dinner at the home of friends here in Romania, when one of their sons, Alex, dropped by. Alex and I have in common that we each have an identical twin. 

Here are my twin brother, Kevin, and I enjoying a cup of coffee. 

Now I speak excellent Romanian after ten years of considerable effort and forced immersion opportunities. But even so, there are native speaker instincts I simply don't have. As a result I will at times say something that no native speaker would.

I stumbled on a case of this in conversation with Alex. When I reference my twin, I frequently refer to him in English as "My Twin." But on two occasions last night, when I asked Alex about "geamănul tau" (your twin),  he asked me, "fratele meu" (my brother)? 

Now, I may reference Kevin as "my twin brother," but I would never just reference him as "my brother," since that simply doesn't, for me, include a key detail about our relationship. 

But Alex seemed to be unaccustomed to using the singular word geamăn. He certainly knows that together they are gemeni, but he consistently just calls him brother/frate.

I puzzled over this and asked my Romanian wife about this. And she felt that the singular as a substantive is not really used in Romanian. She indicated that a native Romanian would probably describe their family in terms such as, "And I have a brother Kevin. We're twins (suntem gemeni)" and not "And I have a twin named Kevin." Another option would be to use the word as an adjective and say, "fratele meu geamăn" (my twin brother).

I did a little research into the Latin antecedent of the Romanian and it really seems that the Romanian instinct is preserving the parent faithfully. Geminus in Latin is an adjective that describes something as "twinned." You have, for instance, the famous quote from Horace about starting stories in medias res (in the middle of things) and not ab ovo:

nec gemino bellum Troianum orditur ab ovo
Nor is the Trojan War recounted from the twin egg
(i.e., starting from the story of how Helen of Troy was born from a twin egg after her mother Leta was seduced by Jupiter in the form of a goose) 
Horace, Ars Poetica, 147

Here are my twin and I out on the town in matching jackets!

Now, there  are cases in which geminus in the singular describes a human twin, but always as an adjective:

soror gemina
A twin sister
Plautus. Mil. 2.4.30

Hic eius geminust frater
This is his twin brother 
Plautus Pers. 5.2.49

Geminus is only used as a full substantive in the plural:

Servilii, qui gemini fuerunt
The Servilii, who were twins
Cicero Ac. 2.18.56

But this got me to thinking about why the Latin geminus can be in the plural at all. Geminus should have been an excellent candidate for preserving the archaic dual. As we have it, the dual survives in Latin only in the words duo (two) and ambo (both). And the reason it got preserved there is that those are both words which, by pure definition, only occur in twos. But don't twins also, by definition occur in twos?

Perhaps the answer lies in the fact that the word geminus, originally meaning twinned, was also put in service to describe further multiple births. Note, for instance, the famous Horatii and Curiatii are described by Livy (1.24.1) as trigemini fratres (triplet brothers).

Finally, for no academic reason whatsoever, here are my twin and I at our cousin's "purple-themed wedding." Hey, we were already dressed in purple. Someone had left some purple wigs lying around. It was not an opportunity to waste. I guess it's a twin thing.