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.