devotion vs novena

devotion and novena both are nouns.

Word	Noun	Adjective	Verb	Adverb
devotion	Yes	No	No	No
novena	Yes	No	No	No

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

devotion: (usually plural) religious observance or prayers (usually spoken silently)
novena: a Roman Catholic devotion consisting of prayers on nine consecutive days

Other hyponyms of devotion include bhakti, Stations, Stations of the Cross.

devotion (noun)	novena (noun)
(usually plural) religious observance or prayers (usually spoken silently)	a Roman Catholic devotion consisting of prayers on nine consecutive days
commitment to some purpose
religious zeal; the willingness to serve God
feelings of ardent love