vocal vs ballad

vocal and ballad both are nouns.

Word	Noun	Adjective	Verb	Adverb
vocal	Yes	Yes	No	No
ballad	Yes	No	No	No

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

vocal (noun)	ballad (noun)
music intended to be performed by one or more singers, usually with instrumental accompaniment	a narrative poem of popular origin
a short musical composition with words	a narrative song with a recurrent refrain

vocal (adjective)	ballad (adjective)
having or using the power to produce speech or sound
relating to or designed for or using the singing voice
given to expressing yourself freely or insistently
full of the sound of voices