tune in vs tune

tune in is not a noun while tune is a noun.

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

As verbs, tune is a hypernym of tune in; that is, tune is a word with a broader meaning than tune in:

tune in: regulate (a radio or television set) in order to receive a certain station or program
tune: adjust for (better) functioning

Other hypernyms of tune in include tune up.

tune in (noun)	tune (noun)
	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

tune in (verb)	tune (verb)
regulate (a radio or television set) in order to receive a certain station or program	adjust the pitches of (musical instruments)
	adjust for (better) functioning