mirage vs optical illusion

mirage and optical illusion both are nouns.

Word	Noun	Adjective	Verb	Adverb
mirage	Yes	No	No	No
optical illusion	Yes	No	No	No

As nouns, optical illusion is a hypernym of mirage; that is, optical illusion is a word with a broader meaning than mirage:

mirage: an optical illusion in which atmospheric refraction by a layer of hot air distorts or inverts reflections of distant objects
optical illusion: an optical phenomenon that results in a false or deceptive visual impression

mirage (noun)	optical illusion (noun)
something illusory and unattainable	an optical phenomenon that results in a false or deceptive visual impression
an optical illusion in which atmospheric refraction by a layer of hot air distorts or inverts reflections of distant objects