I just really don't know where English ex-, as in "ex-friend" exactly came from. So far I havent seen such meaning in Latin (or Greek), but I know little. It would bolster the following idea, if there were the slightest hint of such a meaning in Latin. In the majority of cases it means "out, off, from", which is perhaps close enough, so I'm just asking for curiosity's sake whether "ex-" could mean "old", not just "former", specifically.
I reason thus:
- Indo-European s-mobile is as of yet unexplained, because it appears and disappears without a discernable pattern prefixed to various words in various Indo-European languages. One usual example is taurus ~ En steer. I entertain the idea that *s- was one or various prefixes. I quickly found that *(s)- sometimes corresponds to German aus- "out, off" in a couple of synonyms, and I fixated on the idea that it might be a reduction from "ex-". Not to divert, it doesn't make much sense for a bull to be out. But it would make sense as an ex-taur, e.g. if a steer were a castrated or grown bull; On the one hand, a grown castrated male cattle is rather called ox. On the other hand, indeed, there's the adjective Ger ausgewachsen "grown up". Also, Jung-Bulle is a fixed term, but Jung- is generally productive (linguistically; no pun intended).
On the topic of age, senex came to mind, and I wondered if folk etymology would be liable to split the word and deem the coda the semantic mark.
Goth. sineigs reconstructs PIE *senikos [Kroonen], though all the remaining languages reflect *senus. Just noting, because en.wiktionary doesn't though it seems relevant to senex. They have derived PIE roots from less, so either there was a reason to leave senex with *senus and imply a Proto-Italic development instead or most likely they just didn't catch up with the book-keeping.
By the way: Also cp. G sehnig "sinewy; (of meat) gnarly" (which is indicative of its lived age? Obviously, usually compared to Sehne "tenon", sine, sinus); synonym: zerrig (cf zerren), perhaps figuratively störrisch "stubborn" (cf PIE *ster- "stiff", G starr, stur) though usually said of living animals (for which, incidentally, DWDS gives a similar sense under v. G. zieren, which I likened to tired [discussion]).
By the way: "ex-" is difficult to reconstruct for PIE, giving slightly different alternative forms, and it's one of the very few roots (or paradigms) with an initial vowel.
Different derivations for an s- have been gleamed, and I might be way off anyway. So if the answer is negative, that's expected.
- By the way: cp expectation, Ger Aussicht (lit. "out-sight", "out-look"); Should it be "ex-spect" or did German frequently produce phono-semantic calques or severe folk-etymology?
Lest I be blamed for omitting the question: Is there a phrase, fixed collocation, or even a word that meaningfully compounds a) "ex" and "taurus" in any such way as outlined above, or b) about any other stem with "ex" in the sense "mature, old"?
Basically I was just surprised that Wiktionary gives such a terse gloss for Lat. prep. "ex", because out turned out very polysemous. After all, however, they just need to link [[ex-#English]] directly to the Latin prefix that gives a couple more glosses, which are a better fit, for a start:
ē- + dormiō → ēdormiō
ē- + pōtō → ēpōtō
- (intensive) thoroughly
ē- + dūrus + -ō → ēdūrō
ex- + acuō → exacuō
- denoting achievement
ex- + ōrō → exōrō
ex- + pugnō → expugnō