petitioner vs applicant

petitioner and applicant both are nouns.

Word	Noun	Adjective	Verb	Adverb
petitioner	Yes	No	No	No
applicant	Yes	No	No	No

As nouns, applicant is a hypernym of petitioner; that is, applicant is a word with a broader meaning than petitioner:

petitioner: one praying humbly for something
applicant: a person who requests or seeks something such as assistance or employment or admission

Other hypernyms of petitioner include applier.

petitioner (noun)	applicant (noun)
one praying humbly for something	a person who requests or seeks something such as assistance or employment or admission
someone who petitions a court for redress of a grievance or recovery of a right