noun, masculine/sə.ɡɔ̃.dɑ̃/plural: secondants
second (attendant of a duel or boxing match standing in for a contestant); assistant, coach, trainer
“1798, a letter written in London on the 21 of May, published in Матеріалы, book 3 (1890), page 286” — Upon which Mr Tierney did not say a word; however, the next day he sent a cartel [a written challenge to a duel] to Mr Pitt, who accepted it and went the day before yesterday to the specified place, as did Mr Tierney for his part, each accompanied by his second.