poisonous substance vs toxicant

poisonous substance and toxicant both are nouns.

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

As nouns, poisonous substance and toxicant are synonyms defined as:

poisonous substance and toxicant: any substance that causes injury or illness or death of a living organism

Other synonyms of poisonous substance include poison.

poisonous substance (noun)	toxicant (noun)
any substance that causes injury or illness or death of a living organism	any substance that causes injury or illness or death of a living organism

poisonous substance (adjective)	toxicant (adjective)
	having the qualities or effects of a poison