cattle pen vs pen

cattle pen and pen both are nouns.

Word	Noun	Adjective	Verb	Adverb
cattle pen	Yes	No	No	No
pen	Yes	No	Yes	No

As nouns, pen is a hypernym of cattle pen; that is, pen is a word with a broader meaning than cattle pen:

cattle pen (noun)	pen (noun)
a pen for cattle	female swan
	a writing implement with a point from which ink flows
	an enclosure for confining livestock
	a correctional institution for those convicted of major crimes
	a portable enclosure in which babies may be left to play

cattle pen (verb)	pen (verb)
	produce a literary work