Synonyms for backup

someone who takes the place of another (as when things get dangerous or difficult) (noun)

• stand-in
• substitute
• relief
• reliever
• fill-in

a musical part (vocal or instrumental) that supports or provides background for other musical parts (noun)

• accompaniment
• support

(computer science) a copy of a file or directory on a separate storage device (noun)

the act of providing approval and support (noun)

• backing
• championship
• patronage