man Friday vs helper

man Friday and helper both are nouns.

Word	Noun	Adjective	Verb	Adverb
man Friday	Yes	No	No	No
helper	Yes	No	No	No

As nouns, helper is a hypernym of man Friday; that is, helper is a word with a broader meaning than man Friday:

man Friday: the most helpful assistant
helper: a person who contributes to the fulfillment of a need or furtherance of an effort or purpose

Other hypernyms of man Friday include assistant, help, supporter.

man Friday (noun)	helper (noun)
the most helpful assistant	a person who helps people or institutions (especially with financial help)
	a person who contributes to the fulfillment of a need or furtherance of an effort or purpose