ἅπαξ
Etym. α copul. and root παγ, πήγνυμι, cf. lat. "simplex".
I. "once, once only, once for all", like Lat. semel, Od., Hdt., attic
2. c. gen., ἅπ. τοῦ ἐνιαυτοῦ "once" in the year, Hdt.
II. without any notion of number, after εἴπερ, ἤν, ἐπεί, ὡς, ὅταν, like Lat. ut semel, εἴπερ ἐσπείσω γ᾽ ἅπαξ if "once" you have made a treaty, Ar.; ὡς ἅπαξ ἤρξατο "once" he had begun, Xen.