WordNet (r) 3.0 (2006):

manna from heaven
    n 1: (Old Testament) food that God gave the Israelites during
         the Exodus [syn: miraculous food, manna, manna from
         heaven]
    2: a sudden happening that brings good fortune (as a sudden
       opportunity to make money); "the demand for testing has
       created a boom for those unregulated laboratories where boxes
       of specimen jars are processed like an assembly line" [syn:
       boom, bonanza, gold rush, gravy, godsend, manna
       from heaven, windfall, bunce]