seconder(n = noun.person) - someone who endorses a motion or petition as a necessary preliminary to a discussion or vote;
is a kind of admirer, booster, champion, friend, protagonist, supporter
Derived form verb second1
One who seconds{3} or supports what another attempts, affirms, moves, or proposes; as, the seconder of an enterprise or of a motion. [1913 Webster]
N auxiliary, recruit, assistant, adjuvant, adjutant, ayudante, coaid, adjunct, help, helper, help mate, helping hand, midwife, colleague, partner, mate, confrere, cooperator, coadjutor, coadjutrix, collaborator, ally, friend, confidant, fidus Achates, pal, buddy, alter ego, confederate, accomplice, complice, accessory, accessory after the fact, particeps criminis, socius criminis, aide-de-camp, secretary, clerk, associate, marshal, right-hand, right-hand man, Friday, girl Friday, man Friday, gopher, gofer, candle- holder, bottle-holder, handmaid, servant, puppet, cat's-paw, jackal, tool, dupe, stooge, ame damnee, satellite, adherent, votary, sectarian, secretary, seconder, backer, upholder, abettor, advocate, partisan, champion, patron, friend at court, mediator, angel (theater, entertainment), friend in need, Jack at a pinch, deus ex machina, guardian angel, tutelary genius.