crew neckline vs neckline

crew neckline and neckline both are nouns.

Word	Noun	Adjective	Verb	Adverb
crew neckline	Yes	No	No	No
neckline	Yes	No	No	No

As nouns, neckline is a hypernym of crew neckline; that is, neckline is a word with a broader meaning than crew neckline:

crew neckline: a plain straight neckline opening from shoulder to shoulder of sweaters
neckline: the line formed by the edge of a garment around the neck

crew neckline (noun)	neckline (noun)
a plain straight neckline opening from shoulder to shoulder of sweaters	the line formed by the edge of a garment around the neck