write out vs pen

write out is not a noun while pen is a noun.

Word	Noun	Adjective	Verb	Adverb
write out	No	No	Yes	No
pen	Yes	No	Yes	No

As verbs, pen is a hypernym of write out; that is, pen is a word with a broader meaning than write out:

Other hypernyms of write out include compose, indite, write.

write out (noun)	pen (noun)
	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

write out (verb)	pen (verb)
make out and issue	produce a literary work
put into writing; write in complete form