hemp vs plant fiber

hemp and plant fiber both are nouns.

Word	Noun	Adjective	Verb	Adverb
hemp	Yes	No	No	No
plant fiber	Yes	No	No	No

As nouns, plant fiber is a hypernym of hemp; that is, plant fiber is a word with a broader meaning than hemp:

Other hypernyms of hemp include plant fibre.

hemp (noun)	plant fiber (noun)
a rope that is used by a hangman to execute persons who have been condemned to death by hanging	fiber derived from plants
any plant of the genus Cannabis; a coarse bushy annual with palmate leaves and clusters of small green flowers; yields tough fibers and narcotic drugs
a plant fiber