Herbert Weir Smyth, A Greek Grammar for Colleges

a. ὅτι meaning that was originally, like Hom. ὅ, perhaps an accusative of the inner object (cognate): ὁρῶ ς` νοσεῖς lit. I see what sickness you are sick (= ἣν νόσον νοσεῖς). But by the time of Homer both ὅ and ὅτι had become mere formal conjunctions. Hom. ὅτε that seems to be a weakened ὅτε when; but this is disputed.

b. διότι originally = διὰ τοῦτο, ὅτι on account of this, that = because (as T. 1.52); then = ὅτι that in Hdt. and in Attic after Isocrates, who uses διότι for ὅτι to avoid hiatus.

c. ὡς strictly an old ablative of ὅς (2989) meaning how, in what way, as in exclamatory clauses and indirect questions. The meaning how (cp. how that) may be seen in οἶδα γὰρ ὥς μοι ὀδώδυσται κλυτὸς ἐννοσίγαιος for I know how (that) the famed earth-shaker has been wroth against me ε 423, and also in Attic (And. 2.14; I. 2.3, 3. 10, 16. 11, 16. 15; Aes. 2.35; D. 24.139). The development of ὡς how to ὡς that followed from the use of ὡς after verbs signifying to see, perceive, know, and the like. Cp. “he sayed how there was a knight.”

d. ὅπως (2929) that is common in Herodotus (ὅκως), rare in Attic, most used in poetry and Xenophon. From its original use in indirect questions ὅπως how gradually acquired the meaning that. Thus, ““ἀλλ᾽ ὅπως μὲν . . . ἐγὼ ἄχθομαι ὑ_μᾶς τρέφων, μηδ᾽ ὑπονοεῖτε” do not even entertain the thought that I am annoyed at maintaining you” X. C. 3.3.20.

e. οὕνεκα = οὖ ἕνεκα, for τούτου ἕνεκα, ὅ, properly causal: on account of (as regards) this, that, and then = that, even in Homer (Odyssey and Λ 21) and later in poetry. Thus, ““ἐξάγγελλε . . . οὕνεκ᾽ Οἰδίπους τοιαῦτ᾽ ἔνειμε παισὶ τοῖς αὑτοῦ γέρα_” announce that Oedipus has distributed such honours to his sons” S. O. C. 1393.

f. ὁθούνεκα = ὅτου ἕνεκα, for τούτου ἕνεκα, ὅτι; and then = that. It is found only in tragedy, as ““ἄγγελλε . . . ὁθούνεκα τέθνηκ᾽ Ὀρέστης” report that Orestes is dead” S. El. 47.