covenant of salt
1. archaic An agreement or union between two or more parties meant to be binding and long-lasting. An allusion to such a covenant mentioned in the Bible (especially in II Chronicles 13:15), which is itself a reference to salt's function as a preservative. There is an interminable covenant of salt between the stock market and the whole of the US economy.
2. A traditional ceremony of marriage, in which each person exchanges a pinch of salt into a single receptacle, symbolizing an eternal and binding union. Though the meaning was perhaps lost on our younger guests, the covenant of salt at our wedding was a simple but meaningful symbol of our devotion to a new life together.