cotton fiber vs cotton wool

cotton fiber and cotton wool both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotton fiber	Yes	No	No	No
cotton wool	Yes	No	No	No

As nouns, cotton fiber and cotton wool are synonyms defined as:

cotton fiber and cotton wool: soft silky fibers from cotton plants in their raw state

Other synonyms of cotton fiber include cotton.

cotton fiber (noun)	cotton wool (noun)
soft silky fibers from cotton plants in their raw state	soft silky fibers from cotton plants in their raw state