devotion vs bhakti

devotion and bhakti both are nouns.

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

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

devotion: (usually plural) religious observance or prayers (usually spoken silently)
bhakti: (Hinduism) loving devotion to a deity leading to salvation and nirvana; open to all persons independent of caste or sex

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

devotion (noun)	bhakti (noun)
(usually plural) religious observance or prayers (usually spoken silently)	(Hinduism) loving devotion to a deity leading to salvation and nirvana; open to all persons independent of caste or sex
commitment to some purpose
religious zeal; the willingness to serve God
feelings of ardent love