selenite vs poisonous substance

selenite and poisonous substance both are nouns.

Word	Noun	Adjective	Verb	Adverb
selenite	Yes	No	No	No
poisonous substance	Yes	No	No	No

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

selenite: a compound that contains a SeO32− anion.
poisonous substance: any substance that causes injury or illness or death of a living organism

Other hypernyms of selenite include salt, poison, toxicant.

selenite (noun)	poisonous substance (noun)
a compound that contains a SeO32− anion.	any substance that causes injury or illness or death of a living organism