petitioner
n. C1 Advanced US //pəˈtɪʃənɝ// UK //pətˈɪʃənɐ// pe·ti·tion·er
n. a person who asks a court or a government to make a formal decision or change a law.
n. a person who formally requests a court or government body to perform an action or grant a right.
The petitioner asked the court to change the law.
After the hearing, the petitioner submitted a final brief to the judge to support their request for a new trial.
In many legal systems, the petitioner must demonstrate a clear and present interest in the matter before the court will consider their application for a writ of habeas corpus.
From petition + -er. Doublet of petitionary.