From piōn (fat, rich). Fatness, richness — used metaphorically of the spiritual richness of the olive tree (Israel) into which Gentile believers are grafted.
Paul warns Gentile believers not to boast against the natural branches (Israel), for they share in the 'nourishing richness' of the olive tree (Romans 11:17). Gentile believers are grafted in and share Israel's spiritual heritage. The church does not replace Israel but is grafted into the same root of God's covenant faithfulness.