ἱλαστήριος, ἱλαστηρια, ἱλαστήριον (ἱλάσκομαι, which see), relating to appeasing or expiating, having placating or expiating force, expiatory: μνῆμα ἱλαστήριον, a monument built to propitiate God, Josephus, Antiquities 16, 7, 1; ἱλαστήριος θάνατος, 4Ma 17:22; χεῖρας ἱκετηριους, εἰ βούλει δέ ἱλαστηριους, ἐκτείνας Θεῷ, Niceph. in act. SS. edition Mai, vol. v., p. 335, 17. Neuter τό ἱλαστήριον, as a substantive, a means of appeasing or expiating, a propitiation (German Versöhnungs- oderSühnmittel); cf. Winer’s Grammar, 96 (91); (592 (551)). So used of:

1. the well-known cover of the ark of the covenant in the Holy of holies, which was sprinkled with the blood of the expiatory victim on the annual day of atonement (this rite signifying that the life of the people, the loss of which they had merited by their sins, was offered to God in the blood as the life of the victim, and that God by this ceremony was appeased and their sins were expiated); hence, the lid of expiation, the propitiatory, Vulg.propitiatorium; Luth.Gnadensruhl (A. V. mercy-seat): Heb 9:5 (the Sept. Exo 25:18 ff; Lev 16:2, etc.; more fully ἱλαστήριον ἐπίθεμα, Exo 25:17; Exo 38:7 (Exo 37:6), for the Hebrew ëÇÌôÉÌøÆú, from ëÄÌôÆÌø to cover, namely, sins, i. e. to pardon). Theodoret, Theophylact, Oecumenius, Luther, Grotius, Tholuck, Wilke, Philippi, Umbreit (Cremer (4te Aufl.)) and others give this meaning to the word also in Rom 3:25, viz. that Christ, besprinkled with his own blood, was truly that which the cover or ’mercy-seat’ had been typically, i. e., the sign and pledge of expiation; but in opposed to this interpretation see Fritzsche, Meyer, Van Hengel (Godet, Oltramare) and others at the passage

2. an expiatory sacrifice; a piacular victim (Vulg.propitiatio): Rom 3:25 (after the analogy of the words χαριστηρια sacrifices expressive of gratitude, thank-offerings, σωτηρία sacrifices for safety obtained. On the other hand, in Dio Chrysostom or. 11, 121, p. 355, Reiske edition, the reference is not to a sacrifice but to a monument, as the preceding words show: καταλείψειν γάρ αὐτούς ἀνάθημα κάλλιστον καί μέγιστον τῇ Ἀθηνα καί ἐπιγράψειν, ἱλαστήριον Ἀχαιοι τῇ Ἰλιαδι). (See the full discussion of the word in Dr. Jets. Morison, Critical Exposition of the Third Chapter of the Epistle to the Romans, pp. 281-303.)