sponsor vs backer

sponsor and backer both are nouns.

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

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

sponsor (noun)	backer (noun)
someone who supports or champions something	someone who provides financial support for some venture
an advocate who presents a person (as for an award or a degree or an introduction etc.)

sponsor (verb)	backer (verb)
assume sponsorship of
assume responsibility for or leadership of
do one's shopping at; do business with; be a customer or client of