a person who supports or aids a person, cause, enterprise, etc.

a person who bets on a competitor in a race or contest.

canvas or other material used for backing.

noun

antagonist , opponent , opposer

noun

advocate , ally , angel * , benefactor , champion , endorser , follower , grubstaker , meal ticket * , money , patron , promoter , protagonist , sponsor , staker , underwriter , well-wisher , contributor , friend , supporter , guarantor , guaranty , surety , abettor , angel , cohort , collaborator , colleague , constituent , corroborator , exponent , insurer , investor , proponent , subscriber