Agnus Dei vs emblem

Agnus Dei and emblem both are nouns.

Word	Noun	Adjective	Verb	Adverb
Agnus Dei	Yes	No	No	No
emblem	Yes	No	No	No

As nouns, emblem is a hypernym of Agnus Dei; that is, emblem is a word with a broader meaning than Agnus Dei:

Other hypernyms of Agnus Dei include allegory.

Agnus Dei (noun)	emblem (noun)
figure of a lamb; emblematic of Christ	special design or visual object representing a quality, type, group, etc.
a liturgical prayer beginning with these Latin words	a visible symbol representing an abstract idea