sweater vs turtleneck

sweater and turtleneck both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweater	Yes	No	No	No
turtleneck	Yes	No	No	No

As nouns, turtleneck is a hyponym of sweater; that is, turtleneck is a word with a more specific, narrower meaning than sweater:

Other hyponyms of sweater include cardigan, pullover, slipover, polo-neck, turtle.

sweater (noun)	turtleneck (noun)
a crocheted or knitted garment covering the upper part of the body	a sweater or jersey with a high close-fitting collar
a person who perspires