sulphurous vs caustic

sulphurous is not a noun while caustic is a noun.

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

As adjectives, sulphurous and caustic are synonyms defined as:

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

sulphurous (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

sulphurous (adjective)	caustic (adjective)
of or related to or containing sulfur or derived from sulfur	of a substance, especially a strong acid; capable of destroying or eating away by chemical action
characterized by oppressive heat and humidity	harsh or corrosive in tone
harsh or corrosive in tone