English translation (word)
English translation (etymon)
Ἑταῖρος: Βοηθὸς, συνναύτης, φίλος. Εὔσημος ἡ λέξις κατὰ τὸ δηλούμενον. Παρὰ τὸ ἠθεῖος, ἠθαῖος κατὰ Δωριεῖς, ὡς εἴθε, αἴθε. Ἢ παρὰ τὸ ἦθος, ἠθαῖος, καὶ ἐθαῖος· καὶ κατὰ ἐναλλαγὴν, ἑταῖρος, πλεονασμῷ τοῦ ρ· καὶ τὸ ε δασύνεται. Ἢ ὡς δρόμος δρομαῖος, οὕτως ἔθος ἐθαῖος, ὁ συνήθης· εἶτα μεταθέσει τοῦ θ εἰς τ, ἑταῖος, καὶ πλεονασμῷ τοῦ ρ ὡς στὰξ, στράξ· ἄτεμις, ἄρτεμις· ἴδις, ἴδρις· ἀκοῶμαι, ἀκροῶμαι. Ἢ ἐκ τοῦ ἔθω, ἐθαῖρος· καὶ μεταθέσει τοῦ θ, ὡς θρὶξ τριχὸς, γίνεται ἑταῖρος, ὁ ἐξ ἔθους τινὶ ἐπιφοιτῶν· καὶ ἀποβολῇ τοῦ ι, ἕταρος.
Hetairos "companion": who succours, who is on the same ship, friend. The meaning of the word is clear according to what is meant. From ētheios "trusty", *ēthaios in Doric fashion, as in eithe / aithe "if". Or from ēthos "character", *ēthaios and *ethaios, and through change, hetairos, by adjunction of the [r], and the [e] has a rough breathing. Or, as dromos "race", dromaios "running", so ethos "custom" *ethaios, the customary one, and then with change of the [th] into [t] and addition of [r], as in stax / strax, atemis / Artemis, idis / Idris, akoômai / akroômai. Or from ethō "to be used to", *ethairos, and through change of the [th], as in thrix, trikhos "hair", comes hetairos, the one who is used to frequenting someone. And through dropping of the [I], hetaros.
Derivational etymology relying on the fact that ῆθεῖος is often used in Homer when a character addresses a companion. So that the companion is ἠθεῖος. There is no syntagmatic co-occurrence of ἠθεῖος and ἑταῖρος in Homer, but rather a paradigmatic association which could lead to the one being interpreted as the etymon of the other. Notice that here the rare word is given as etymon of the usual one. The etymology implies several formal manipulations, explicit in the Etym. Magnum.
There is no parallel
NB: the etymological notice in Beekes' EDG is contradictory about the relationship with ἔτης. On the one hand, ἑταῖρος shows no trace of initial ϝ, whereas ϝέτης does, but given the various reflexes of initial *sw- in Greek, this is not a very strong objection.