composition vs song

composition and song both are nouns.

Word	Noun	Adjective	Verb	Adverb
composition	Yes	No	No	No
song	Yes	No	No	No

As nouns, song is a hyponym of composition; that is, song is a word with a more specific, narrower meaning than composition:

composition (noun)	song (noun)
the act of creating written works	the act of singing
musical creation	a short musical composition with words
something that is created by arranging several things to form a unified whole	the characteristic sound produced by a bird
the way in which someone or something is composed	a distinctive or characteristic sound
the spatial property resulting from the arrangement of parts in relation to each other and to the whole	a very small sum
an essay (especially one written as an assignment)
a musical work that has been created
art and technique of printing with movable type
a mixture of ingredients