The food of the gods (Greek, a privative, brotos, mortal); so called because it made them not mortal, i.e. it made them immortal. Anything delicious to the taste or fragrant in perfume is so called from the notion that whatever is used by the celestials must be excellent.
“A table where the heaped ambrosia lay.”
Homer, by Bryant: Odyssey , v. line 141.
“Husband and wife must drink from the cup of conjugal life; but they must both taste the same ambrosia, or the same gall.”
R. C. Houghton: Women of the Orient , part iii.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894