opposant
/əˈpəʊz(ə)nt/rare
noun
= opponent. In later use: ( Canadian Law ) a person contesting a matter before a judge or court.
Origin
Late 15th century; earliest use found in William Caxton (1415x24–1492), printer, merchant, and diplomat. From French opposant, use as noun of present participle of opposer oppose; compare -ant.