ἐπεί
conjunct., temporal and causal, like Lat. quum:
A. OF TIME, "after that, after (postquam), since, when (quum)", with aor. to express a complete action, or imperf. to express one not yet complete, ἐπεὶ ὑπηντίαζεν ἡ φάλαγξ καὶ ἡ σάλπιγξ ἐφθέγξατο "after" the phalanx "began" to advance and the trumpet "had" sounded, Xen.
2. = ἐξ οὗ, "from the time when, ever since", ἐπείτε παρέλαβον τὸν θρόνον "since" I came to the throne, Hdt.
II. with Subjunct., ἄν or κε being added, so that ἐπεί becomes ἐπάν, ἐπήν, ionic ἐπεάν, or ἐπεί κε: — referring to future time, ἐπὴν ἕλωμεν "when" we shall have taken the city, Il.:—also "whenever", ἐπεί κε λίπῃ ὀστέα θυμός Od.
III. with Opt. without ἄν, referring to future time, ἐπειδὴ πρὸς τὸ φῶς ἔλθοι "after" he had come into the light, Plat.:—also "whenever", ἐπεὶ πύθοιτο Xen.
2. in oratione obl. after past tenses, representing a subj. in orat. rect., ἐπεὶ διαβαίης, the direct form being ἐπὴν διαβῶ, id=Xen.
IV. with other words, ἐπεὶ τάχιστα, "as soon as", Lat. quum primum, id=Xen.; ἐπεὶ εὐθέως id=Xen.; ἐπειδὴ τάχιστα Plat.; ἐπειδὴ θᾶττον Dem.
B. CAUSAL, "since, seeing that", with Ind. or Opt. with ἄν, Hom., etc.; with Imp., ἐπεὶ δίδαξον "for" teach me, Soph.; ἐπεὶ πῶς ἂν καλέσειας; "for" how would you call him? Ar.:—sometimes it may be rendered by "although", or by "else, otherwise."
2. with other Particles, ἐπεὶ ἄρα, ἐπεὶ ἂρ δή "since" then, Od.; ἐπεί γε, Lat. quandoquidem, since indeed, Hdt.; ἐπείπερ "seeing that", Aesch., etc.; ἐπεί τοι "since" surely, Soph.