vegetable silk vs plant fiber

vegetable silk and plant fiber both are nouns.

Word	Noun	Adjective	Verb	Adverb
vegetable silk	Yes	No	No	No
plant fiber	Yes	No	No	No

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

vegetable silk: a plant fiber from the kapok tree; used for stuffing and insulation
plant fiber: fiber derived from plants

Other hypernyms of vegetable silk include plant fibre.

vegetable silk (noun)	plant fiber (noun)
a plant fiber from the kapok tree; used for stuffing and insulation	fiber derived from plants