sweater vs cardigan

sweater and cardigan both are nouns.

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

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

sweater: a crocheted or knitted garment covering the upper part of the body
cardigan: knitted jacket that is fastened up the front with buttons or a zipper

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

sweater (noun)	cardigan (noun)
a crocheted or knitted garment covering the upper part of the body	knitted jacket that is fastened up the front with buttons or a zipper
a person who perspires