allegiance vs devotion

allegiance and devotion both are nouns.

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

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

allegiance: the act of binding yourself (intellectually or emotionally) to a course of action
devotion: commitment to some purpose

Other hyponyms of allegiance include communalism, consecration, enlistment, faith.

allegiance (noun)	devotion (noun)
the act of binding yourself (intellectually or emotionally) to a course of action	(usually plural) religious observance or prayers (usually spoken silently)
the loyalty that citizens owe to their country (or subjects to their sovereign)	commitment to some purpose
	religious zeal; the willingness to serve God
	feelings of ardent love