anonym vs nom de plume

anonym and nom de plume both are nouns.

Word	Noun	Adjective	Verb	Adverb
anonym	Yes	No	No	No
nom de plume	Yes	No	No	No

As nouns, nom de plume is a hyponym of anonym; that is, nom de plume is a word with a more specific, narrower meaning than anonym:

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

Other hyponyms of anonym include stage name, pen name, hagionym.

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