crew neckline vs crew neck

crew neckline and crew neck both are nouns.

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

As nouns, crew neckline and crew neck are synonyms defined as:

crew neckline and crew neck: a plain straight neckline opening from shoulder to shoulder of sweaters

crew neckline (noun)	crew neck (noun)
a plain straight neckline opening from shoulder to shoulder of sweaters	a plain straight neckline opening from shoulder to shoulder of sweaters