Henry George Liddell, Robert Scott, A Greek-English Lexicon

A.once, once only, once for all, first in Od., “ὅτε τ᾽ ἄλλοι ἅ. θνῄσκουσ᾽ ἄνθρωποι” 12.22; ἅ. . . ἀπὸ θυμὸν ὀλέσσαι ib.350; “ἀπαλλάχθηθ᾽ ἅ.” E.Cyc.600; οὐχ ἅ. μόνον more than once, A.Pr.211; “ἅ. . . κοὐχὶ δίς” S.OC1208; “πολλάκις καὶ οὐχὶ ἅ.” Hdt.7.46; “πολλάκις τε κοὐχ ἅ.” S.OT1275; “μὴ ἅ. ἀλλὰ πολλάκις” Antipho 1.3, cf. Pl.Lg.711a; “μὴ δίς, ἀλλ᾽ ἅ. μόνον” Arist.Pol.1299a10; of the self-creation of “Νοῦς, τὴν ποίησιν αὑτοῦ . . ἅ. εἶναι” Plot.6.8.21; ἅ. ἔτι yet this once, A.Ag.1322; τὸ ἅ. τοῦτο at this moment, LXX2 Ki.17.7; ἅ. δυοῖν ποδοῖν, i.e. two square feet (1 x 2), opp. δυοῖν δίς (2 x 2), four, Pl.Men.82c.

2. c. gen., ἅ. τοῦ ἐνιαυτοῦ, ἔτεος ἑκάστου ἅ., Hdt.2.59, 4.105; also “ἐν τῷ ἐνιαυτῷ ἅ.” Id.2.132.

3. once on a time, formerly, “ἅ. καὶ ἅ.” LXXJd.20.30.

II. without any notion of number, after conditional and temporal Particles, if once, when once, εἴπερ ἐσπείσω γ᾽ ἅ. if once you have made a treaty, Ar.Ach.307. cf. 923; “ἢν ἅ. ἁλῷ” Id.V.898, cf. Av.342; “ἂν ἅ. τις ἀποθάνῃ” Amphis 8; “ἐπειδήπερ γ᾽ ἅ. ἐμοὶ σεαυτὸν παραδέδωκας” Ar.V.1129; “ἐπεὶ ἅ. ἐταράχθησαν” Th.7.44; “ὡς ἅ. ἤρξατο” X.HG5.4.58; “ἐπεὶ ἅ. αὐτοῖς φίλος ἐγένετο” Id.An.1.9.10, cf. 3.2.25, Isoc.12.242; “ὡς ἅ. ἐγκλήματα ἐταράχθη” D.18.151: so with part., “ἐπὶ γᾶν ἅ. πεσὸν . . . αἷμα” A.Ag.1019(lyr.); “ἅ. θανόντος οὔτις ἔστ᾽ ἀνάστασις” Id.Eu.648; “ἅ. ἐλθόντες” Pl.Prm.165e, cf. Ep.Hebr.6.4, etc. (ἁ- = sṃ (cf. εἷς）; -παξ akin to πήγνυμι.）