268. This conjunction (which may be treated as a single word) is used in two ways
a. To assign a cause or reason.
b. To connect the fact expressed in the relative clause with a verb of saying, knowing, etc.
The second of these uses is evidently derived from the first by a kind of degeneration, or loss of meaning. The fact told or known is originally given as the ground of the saying or knowing. The transition may be seen in
Od. 7.299 ξεῖνʼ, ἦ τοι μὲν τοῦτό γʼ ἐναίσιμον οὐκ ἐνόησε
παῖς ἐμή, οὕνεκά σʼ οὔ τι μετʼ ἀμφιπόλοισι γυναῖξιν
ἦγεν ἐς ἡμέτερον
my daughter did not judge aright in this, because she did not, etc.
more simply, in this, that she did not, etc. Again
Od. 5.215 οἶδα καὶ αὐτὸς
πάντα μάλʼ, οὕνεκα σεῖο περίφρων Πηνελόπεια κτλ.
I know all, inasmuch as Penelope is, etc.
i.e. I know that she is. This use is found with verbs of saying in Od. 13.309, 15.42, 16.330, 379. In the Iliad it occurs only once.
Il. 11.21 πεύθετο . . . μέγα κλέος, οὕνεκʼ Ἀχαιοί κτλ.
Note that (except in Od. 13.309, 16.379) the verb is followed by an accusative of the thing; so that the relative clause does not directly take the place of the object. Thus (e. g.) πεύθετο κλέος οὕνεκα is literally heard a rumor the ground of which was that, etc.
A peculiar use to state a consequence which is made the ground of inference may be seen in
Il. 9.505 ἡ δʼ Ἄτη σθεναρή τε καὶ ἀρτίπος, οὕνεκα πάσας
Ate is strong and sound of fοοt, (as we knοw) because she, etc.