cage vs iron cage

cage and iron cage both are nouns.

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

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

cage (noun)	iron cage (noun)
an enclosure made or wire or metal bars in which birds or animals can be kept	a cage from which there is no escape
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

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