supporter vs backer

supporter and backer both are nouns.

Word	Noun	Adjective	Verb	Adverb
supporter	Yes	No	No	No
backer	Yes	No	No	No

As nouns, backer is a hyponym of supporter; that is, backer is a word with a more specific, narrower meaning than supporter:

supporter (noun)	backer (noun)
a band (usually elastic) worn around the leg to hold up a stocking (or around the arm to hold up a sleeve)	someone who provides financial support for some venture
a support for the genitals worn by men engaging in strenuous exercise
a person who backs a politician or a team etc.
a person who contributes to the fulfillment of a need or furtherance of an effort or purpose
someone who supports or champions something