carnival vs festival

carnival and festival both are nouns.

Word	Noun	Adjective	Verb	Adverb
carnival	Yes	No	No	No
festival	Yes	No	No	No

As nouns, festival is a hypernym of carnival; that is, festival is a word with a broader meaning than carnival:

carnival: a festival marked by merrymaking and processions
festival: an organized series of acts and performances (usually in one place)

Other hypernyms of carnival include fete.

carnival (noun)	festival (noun)
a festival marked by merrymaking and processions	an organized series of acts and performances (usually in one place)
a traveling show; having sideshows and rides and games of skill etc.	a day or period of time set aside for feasting and celebration
a frenetic disorganized (and often comic) disturbance suggestive of a large public entertainment