virulent vs caustic

virulent is not a noun while caustic is a noun.

Word	Noun	Adjective	Verb	Adverb
virulent	No	Yes	No	No
caustic	Yes	Yes	No	No

As adjectives, virulent and caustic are synonyms defined as:

Other synonyms of virulent include acerb, acerbic, acid, acrid, bitter, blistering, sulfurous, sulphurous, vitriolic.

virulent (noun)	caustic (noun)
	the envelope of light rays reflected or refracted by a curved surface or object
	any chemical substance that burns or destroys living tissue

virulent (adjective)	caustic (adjective)
infectious; having the ability to cause disease	of a substance, especially a strong acid; capable of destroying or eating away by chemical action
extremely poisonous or injurious; producing venom	harsh or corrosive in tone
harsh or corrosive in tone