pen vs sheepfold

pen and sheepfold both are nouns.

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

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

pen (noun)	sheepfold (noun)
female swan	a pen for sheep
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

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