petitioner

Concise Oxford English Dictionary © 2008 Oxford University Press:
petition/pəˈtɪʃn/

▶noun

• 1 a formal written request, typically signed by many people, appealing to authority in respect of a cause.

  ■ an appeal or request.

• 2 Law an application to a court for a writ, judicial action in a suit, etc.

▶verb make or present a petition to.

– derivatives
petitionary adjective,
petitioner noun.

– origin ME: from L. petitio(n-), from petit-, petere ‘aim at, seek, lay claim to’.