ἱλάσκομαι

(see below); in classical Greek the middle of an act. ἱλάσκω (to render propitious, appease) never met with;
1. to render propitious to oneself, to appease, conciliate to oneself (from ἴλαος gracious, gentle); from Homer down; mostly with the accusative of a person, as Θεόν, Ἀθηνην, etc. (τόν Θεόν ἱλάσασθαι, Josephus, Antiquities 6, 6, 5); very rarely with the accusative of the thing, as τήν ὀργήν, Plutarch, Cat. min. 61 (with which cf. ἐξιλάσκεσθαι θυμόν, Prov 16:14 the Sept.). In Biblical Greek used passively, to become propitious, be placated or appeased; in 1 aorist imperative ἱλάσθητι, be propitious, be gracious, be merciful (in secular authors ἱληθι and Doric, ἵλαθι, which the gramm. regard as the present of an unused verb ἵλημι, to be propitious; cf. Alexander Buttmann (1873) Ausf. Sp. ii., p. 206; Kühner, § 343, i., p. 839; Passow, (or Liddell and Scott, or Veitch) under the word ἵλημι), with the dative of the thing or the person: Lk 18:13 (ταῖς ἁμαρτίαις, Ps 78:9; Psalm 87:38 (Ps. 88:38>); τῇ ἁμαρτία, Psalm 24:11; ἱλάσθη ὁ κύριος περί τῆς κακίας, Ex 32:14 Alex.; ἱλασθήσεται κυρίου τῷ δούλῳ σου, 2 Kgs 5:18).
2. by an Alexandrian usage, to expiate, make propitiation for (as ἐξιλάσκεσθαι in the O. T.): τάς ἁμαριτας, Heb 2:17 (ἡμῶν τάς ψυχάς, Philo, alleg. leg. 3, 61). (Cf. Kurtz, Commentary on Hebrews, at the passage cited; Winer's Grammar, 227 (213); Westcott, Epistles of St. John, p. 83f.)