byname vs moniker

byname and moniker both are nouns.

Word	Noun	Adjective	Verb	Adverb
byname	Yes	No	No	No
moniker	Yes	No	No	No

As nouns, byname and moniker are synonyms defined as:

byname and moniker: a familiar name for a person (often a shortened version of a person's given name)

Other synonyms of byname include cognomen, nickname, sobriquet, soubriquet.

byname (noun)	moniker (noun)
a familiar name for a person (often a shortened version of a person's given name)	a familiar name for a person (often a shortened version of a person's given name)