cast-iron vs iron

cast-iron is not a noun while iron is a noun.

Word	Noun	Adjective	Verb	Adverb
cast-iron	No	Yes	No	No
iron	Yes	Yes	Yes	No

As adjectives, cast-iron and iron are synonyms defined as:

cast-iron (noun)	iron (noun)
	home appliance consisting of a flat metal base that is heated and used to smooth cloth
	a golf club that has a relatively narrow metal head
	implement used to brand live stock
	a heavy ductile magnetic metallic element; is silver-white in pure form but readily rusts; used in construction and tools and armament; plays a role in the transport of oxygen by the blood

cast-iron (adjective)	iron (adjective)
extremely robust	extremely robust

cast-iron (verb)	iron (verb)
	press and smooth with a heated iron