useless, unprofitable, ἀχρήϊος ἀνήρ Hes. Op. 297; ἐπέων νομός ib. 403; δέμας A. Pr. 365, cf. Hp. Int. 39; οἰκητήρ S. OC 627; opp. εὐγενής, Id. Fr. 667; ἐρινὸς ἀ. ὢν ἐς βρῶσιν ib. 181; ἀ. κοὐ σοφός E. Med. 299; δοῦλος Ev.Matt. 25.30; οὐκ ἀπράγμονα ἀλλʼ ἀχρεῖον νομίζομεν Th. 2.40; λόγον ἀχρεῖον ἀπέρριψαν Ant.Lib. 11.3: Comp. -ότερος, ὄρνιθες Chrysipp.Stoic. 3.195: c. inf., unfit to do, ἀ. πράττειν τι Pl. R. 371c: c. dat., ἀ. τοῖς σώμασι Agatharch. Fr.Hist. 3, cf. Them. Or. 26.326a.
esp. unfit for war, ἀ. ὅμιλος Hdt. 3.81; τὸ ἀ. τοῦ στρατοῦ the unserviceable part of an army, Id. 1.191; οἱ ἀχρειότατοι Th. 1.93, 2.6, cf. X. HG 7.2.18; τὸ ἀ. τῆς ἡλικίας Th. 2.44. Adv. -είως, ἔχειν πρὸς ναυμαχίαν App. BC 5.84.
neut. ἀχρεῖον, as Adv., twice in Hom., ἀχρεῖον ἰδών giving a helpless look, looking foolish, of Thersites after being beaten, Il. 2.269; ἀχρεῖον δʼ ἐγέλασσε laughed without cause, made a forced laugh, of Penelope trying to disguise her feelings, Od. 18.163; ἀχρεῖον κλάζειν bark without need or cause, Theoc. 25.72.
Adv. ἀχρείως γέλασόν με (cf. ἀχρειόγελως) APl. 16.86, cf. Them. Or. 33.367b: neut. pl. as Adv. ἀχρεῖʼ ἀσπαίροντος helplessly, Euph. 44.