Does ξυνήιος, as in
οὐδέ τί που ἴδμεν ξυνήϊα κείμενα πολλά (verse 124)
have anything to do with the ξυνέηκε in
τίς τ’ ἄρ σφωε θεῶν ἔριδι ξυνέηκε μάχεσθαι
(verse 8 ) ?
ξυνέηκε comes from σύν/ξύν + ἵημι.
σύν/ξύν is certainly the first element in ξυνήϊα, but the rest doesn’t look like anything derived from ἵημι. Pulleyn’s commentary on book I and (apparently) Chantraine’s etymological dictionary both think it’s an expanded form of ξυνός “common”.
I myself would have thought that -ήιος is the same as in ἤια, “food provision for a journey”, as in both words there’s the idea of stocking something. But the authorities don’t seem to agree with me.
Surely συν/ξυν has nothing to do with it. ξυνηιος (long υ) must be the ionic form of ξυνειος—unattested, to be sure, but clearly equivalent to ξυνός (long υ) = κοινός. Cf. e.g. ξυνήων (Hesiod; Attic ξυνών), ξυνωνίη (Archilochus), etc., all consistently with long υ (and always with ξ, not σ), whereas the υ in συν/ξυν is never (I think) lengthened.
So I have to disagree with Paul’s “σύν/ξύν is certainly the first element in ξυνήϊα”, and the answer to strnbrg’s question is No, nothing at all.
Chantraine derives ξυνός from *ξυν-yο-, which would give the long υ (compensatory lengthening or whatever). Or do you find something wrong with that? But you’re right to point out the long υ, which I didn’t give proper attention - it can’t be just σύν/ξύν + something because of the long υ.
If that’s right, it does have something to do with it, but you have to go further back to find it, into the realms of philological speculation. I was simply pointing out the quantitative distinction, which appears to be absolute.
Is Chantraine’s postulated glide just a guess (an obvious, even facile one), relying on the semantic similarity, or does it have a proper philological basis? Why should this cluster of words have yod in the first place (and then retain its effect: we don’t find short-υ ξυνός for example), when none of the multitudinous other συν/ξυν- words do? The same question applies if it’s not compensatory but simply metrical lengthening (metrische Dehnung), so why postulate the yod at all?
Your point about the long υ is taken!
As to the rest, the yod and all that : I dunno. 