melody vs tune

melody and tune both are nouns.

Word	Noun	Adjective	Verb	Adverb
melody	Yes	No	No	No
tune	Yes	No	Yes	No

As nouns, melody and tune are synonyms defined as:

Other synonyms of melody include air, line, melodic line, melodic phrase, strain.

melody (noun)	tune (noun)
the perception of pleasant arrangements of musical notes	the adjustment of a radio receiver or other circuit to a required frequency
a succession of notes forming a distinctive sequence	the property of producing accurately a note of a given pitch
	a succession of notes forming a distinctive sequence

melody (verb)	tune (verb)
	adjust the pitches of (musical instruments)
	adjust for (better) functioning