Roman collar vs neckband

Roman collar and neckband both are nouns.

Word	Noun	Adjective	Verb	Adverb
Roman collar	Yes	No	No	No
neckband	Yes	No	No	No

As nouns, neckband is a hypernym of Roman collar; that is, neckband is a word with a broader meaning than Roman collar:

Roman collar: a stiff white collar with no opening in the front; a distinctive symbol of the clergy
neckband: a band that fits around the neck and is usually folded over

Other hypernyms of Roman collar include collar.

Roman collar (noun)	neckband (noun)
a stiff white collar with no opening in the front; a distinctive symbol of the clergy	a band that fits around the neck and is usually folded over
	necklace that fits tightly around a woman's neck
	a band around the collar of a garment