an optical phenomenon, esp. in the desert or at sea, by which the image of some object appears displaced above, below, or to one side of its true position as a result of spatial variations of the index of refraction of air.

something illusory, without substance or reality.

( initial capital letter ) Military . any of a series of supersonic, delta-wing, multirole French fighter-bombers.

noun

delusion , fantasy , hallucination , ignis fatuus , illusion , optical illusion , phantasm , phantasma , will-o\'-the-wisp , corposant , deception , dream , fata morgana , vision