I was preaching on 1 John 1:8- 2:6 this Sunday and found this word ἱλασμος in 2:1 "He is the atoning sacrifice for our sins". The best translation I can find is 'the means of forgiveness' while the NIV translates it with 'atoning sacrifice' in this context. I think the idea of sacrifice is picked up from the Old Testament use of sacrifices as the means of atonement. Apparently the use of this word in the Septuagint relates to the mercy seat of God.
In the previous days this was translated 'propitiation' and had to do with turning away the wrath of God. I suppose that 'means of forgiveness' does imply a turning away of wrath, but I'm not sure that the ideas are conceptually the same. 'Means of forgiveness' leaves a sense of mystery as to the workings of God and how Jesus' life and death worked our salvation.
This word is only also found in 1 John 4:10 in the New Testament. In the Septuagint it is found in Ezekiel 44:27, Psalm 130:4, Lev 25:9, Numbers 5:8 and Amos 8:14 where it is used in diverse contexts.
This could be an interesting study to pursue . . .
(much information from http://m.katabiblon.com/lexicon.php?search=ιλασμος)