pig iron vs cinder pig

pig iron and cinder pig both are nouns.

Word	Noun	Adjective	Verb	Adverb
pig iron	Yes	No	No	No
cinder pig	Yes	No	No	No

As nouns, cinder pig is a hyponym of pig iron; that is, cinder pig is a word with a more specific, narrower meaning than pig iron:

Other hyponyms of pig iron include basic iron, mine pig, spiegel, spiegel iron, spiegeleisen.

pig iron (noun)	cinder pig (noun)
crude iron tapped from a blast furnace	pig iron containing a substantial proportion of slag