melodic theme vs tune

melodic theme and tune both are nouns.

Word	Noun	Adjective	Verb	Adverb
melodic theme	Yes	No	No	No
tune	Yes	No	Yes	No

As nouns, tune is a hypernym of melodic theme; that is, tune is a word with a broader meaning than melodic theme:

Other hypernyms of melodic theme include air, line, melodic line, melodic phrase, melody, strain.

melodic theme (noun)	tune (noun)
(music) melodic subject of a musical composition	the adjustment of a radio receiver or other circuit to a required frequency
	the property of producing accurately a note of a given pitch
	a succession of notes forming a distinctive sequence

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