prayer vs petition

prayer and petition both are nouns.

Word	Noun	Adjective	Verb	Adverb
prayer	Yes	No	No	No
petition	Yes	No	Yes	No

As nouns, prayer and petition are synonyms defined as:

Other synonyms of prayer include orison.

prayer (noun)	petition (noun)
the act of communicating with a deity (especially as a petition or in adoration or contrition or thanksgiving)	a formal message requesting something that is submitted to an authority
earnest or urgent request	reverent petition to a deity
a fixed text used in praying
reverent petition to a deity
someone who prays to God

prayer (verb)	petition (verb)
	write a petition for something to somebody; request formally and in writing