sulfur vs sulfurous

sulfur is a noun but sulfurous is not a noun.

Word	Noun	Adjective	Verb	Adverb
sulfur	Yes	No	Yes	No
sulfurous	No	Yes	No	No

sulfur (noun)	sulfurous (noun)
an abundant tasteless odorless multivalent nonmetallic element; best known in yellow crystals; occurs in many sulphide and sulphate minerals and even in native form (especially in volcanic regions)

sulfur (adjective)	sulfurous (adjective)
	of or related to or containing sulfur or derived from sulfur
	characterized by oppressive heat and humidity
	harsh or corrosive in tone

sulfur (verb)	sulfurous (verb)
treat with sulphur in order to preserve