iron cage vs cage

iron cage and cage both are nouns.

Word	Noun	Adjective	Verb	Adverb
iron cage	Yes	No	No	No
cage	Yes	No	Yes	No

As nouns, cage is a hypernym of iron cage; that is, cage is a word with a broader meaning than iron cage:

iron cage (noun)	cage (noun)
a cage from which there is no escape	an enclosure made or wire or metal bars in which birds or animals can be kept
	the net that is the goal in ice hockey
	a movable screen placed behind home base to catch balls during batting practice
	something that restricts freedom as a cage restricts movement

iron cage (verb)	cage (verb)
	confine in a cage