shoulder board vs epaulette

shoulder board and epaulette both are nouns.

Word	Noun	Adjective	Verb	Adverb
shoulder board	Yes	No	No	No
epaulette	Yes	No	No	No

As nouns, epaulette is a hypernym of shoulder board; that is, epaulette is a word with a broader meaning than shoulder board:

shoulder board: epaulets that indicate rank
epaulette: adornment consisting of an ornamental cloth pad worn on the shoulder

Other hypernyms of shoulder board include epaulet.

shoulder board (noun)	epaulette (noun)
epaulets that indicate rank	adornment consisting of an ornamental cloth pad worn on the shoulder