anonym vs pen name

anonym and pen name both are nouns.

Word	Noun	Adjective	Verb	Adverb
anonym	Yes	No	No	No
pen name	Yes	No	No	No

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

anonym: a fictitious name used when the person performs a particular social role
pen name: an author's pseudonym

Other hyponyms of anonym include stage name, nom de plume, hagionym.

anonym (noun)	pen name (noun)
a fictitious name used when the person performs a particular social role	an author's pseudonym