dad vs pa

dad and pa both are nouns.

Word	Noun	Adjective	Verb	Adverb
dad	Yes	No	No	No
pa	Yes	No	No	No

As nouns, dad and pa are synonyms defined as:

Other synonyms of dad include dada, daddy, papa, pappa, pop.

dad (noun)	pa (noun)
an informal term for a father; probably derived from baby talk	an informal term for a father; probably derived from baby talk