stubble vs plant substance

stubble and plant substance both are nouns.

Word	Noun	Adjective	Verb	Adverb
stubble	Yes	No	No	No
plant substance	Yes	No	No	No

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

stubble: material consisting of seed coverings and small pieces of stem or leaves that have been separated from the seeds
plant substance: material derived from plants

Other hypernyms of stubble include plant material.

stubble (noun)	plant substance (noun)
short stiff hairs growing on a man's face when he has not shaved for a few days	material derived from plants
material consisting of seed coverings and small pieces of stem or leaves that have been separated from the seeds