Abet
to help someone do something wrong or illegal
Advocate
to publicly say that something should be done
Ancillary
auxiliary, supporting, secondary
Bolster
to improve something by making stronger
Corroborate
to provide info that supports someone’s statement
Countenance
to accept, support, or approve of something
Espouse
to support an idea, belief etc, especially a political one
Mainstay
an important part of something, a person who does most of important work
Munificent
very generous
Proponent
someone who supports something or persuades people to do something
Stalwart
someone very loyal