sobriquet vs byname

sobriquet and byname both are nouns.

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

As nouns, sobriquet and byname are synonyms defined as:

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

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

sobriquet (noun)	byname (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)