hymn vs pean

hymn and pean both are nouns.

Word	Noun	Adjective	Verb	Adverb
hymn	Yes	No	Yes	No
pean	Yes	No	No	No

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

hymn: a song of praise (to God or to a saint or to a nation)
pean: (ancient Greece) a hymn of praise (especially one sung in ancient Greece to invoke or thank a deity)

Other hyponyms of hymn include dithyramb, doxology, choral, chorale, canticle, hymeneal, paean, recessional.

hymn (noun)	pean (noun)
a song of praise (to God or to a saint or to a nation)	a formal expression of praise
	(ancient Greece) a hymn of praise (especially one sung in ancient Greece to invoke or thank a deity)

hymn (verb)	pean (verb)
praise by singing a hymn
sing a hymn