church year vs twelvemonth

church year and twelvemonth both are nouns.

Word	Noun	Adjective	Verb	Adverb
church year	Yes	No	No	No
twelvemonth	Yes	No	No	No

As nouns, twelvemonth is a hypernym of church year; that is, twelvemonth is a word with a broader meaning than church year:

church year: the year in the ecclesiastical calendar; especially feast days and special seasons
twelvemonth: a period of time containing 365 (or 366) days

Other hypernyms of church year include year, yr.

church year (noun)	twelvemonth (noun)
the year in the ecclesiastical calendar; especially feast days and special seasons	a period of time containing 365 (or 366) days