The Greek apobolē means rejection, loss, or the act of throwing away / casting off. From apoballo (to throw away, cast off), it appears only twice in the New Testament: once for Israel's rejection of the gospel (Romans 11:15) and once for the 'loss' of lives at sea (Acts 27:22).
Romans 11:15 contains one of Paul's most astonishing theological turns: 'For if their rejection (apobolē) is the reconciliation of the world, what will their acceptance be but life from the dead?' The apobolē of Israel — their setting aside as covenant bearers of the gospel — became the occasion for the gospel to spread to all nations. Paul's 'how much more' logic is stunning: if Israel's loss brought the Gentiles riches, imagine what Israel's full restoration will bring. This word sits at the heart of Paul's theology in Romans 9-11, maintaining both divine sovereignty in the apparent 'rejection' and hope for Israel's future redemption. God's apparent losses are always moving toward greater gains.