prayer vs invocation

prayer and invocation both are nouns.

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

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

prayer (noun)	invocation (noun)
the act of communicating with a deity (especially as a petition or in adoration or contrition or thanksgiving)	the act of appealing for help
earnest or urgent request	calling up a spirit or devil
a fixed text used in praying	a prayer asking God's help as part of a religious service
reverent petition to a deity	an incantation used in conjuring or summoning a devil
someone who prays to God