man Friday vs chief assistant

man Friday and chief assistant both are nouns.

Word	Noun	Adjective	Verb	Adverb
man Friday	Yes	No	No	No
chief assistant	Yes	No	No	No

As nouns, man Friday and chief assistant are synonyms defined as:

Other synonyms of man Friday include right-hand man.

man Friday (noun)	chief assistant (noun)
the most helpful assistant	the most helpful assistant