device vs emblem

device and emblem both are nouns.

Word	Noun	Adjective	Verb	Adverb
device	Yes	No	No	No
emblem	Yes	No	No	No

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

device: an emblematic design (especially in heraldry)
emblem: special design or visual object representing a quality, type, group, etc.

device (noun)	emblem (noun)
any clever maneuver	special design or visual object representing a quality, type, group, etc.
an instrumentality invented for a particular purpose	a visible symbol representing an abstract idea
an emblematic design (especially in heraldry)
any ornamental pattern or design (as in embroidery)
something in an artistic work designed to achieve a particular effect