religious song vs song

religious song and song both are nouns.

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

As nouns, song is a hypernym of religious song; that is, song is a word with a broader meaning than religious song:

Other hypernyms of religious song include church music, religious music, vocal.

religious song (noun)	song (noun)
religious music for singing	the act of singing
	a short musical composition with words
	the characteristic sound produced by a bird
	a distinctive or characteristic sound
	a very small sum