right-hand man vs helper

right-hand man and helper both are nouns.

Word	Noun	Adjective	Verb	Adverb
right-hand man	Yes	No	No	No
helper	Yes	No	No	No

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

right-hand man: 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 right-hand man include assistant, help, supporter.

right-hand man (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