1) relating to an appeasing or expiating, having placating or expiating force, expiatory; a means of appeasing or expiating, a propitiation
1a) used of the 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 expiated); hence the lid of expiation, the propitiatory
1b) an expiatory sacrifice
1c) a expiatory victim
Part of Speech: noun neuter
Citing in TDNT: 3:318, 362
Neuter of a derivative of G2433; an expiatory (place or thing), that is, (concretely) an atoning victim, or (specifically) the lid of the Ark (in the Temple): - mercyseat, propitiation.
|a means of forgiveness||40.12|
|b place of forgiveness||40.13|
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root ἱλαστήριον; click on the second column to search for that grammatical form of the root ἱλαστήριον; click on the third column to search for that word and grammatical form; click on the total to search for the root ἱλαστήριον.