ringer

Concise Oxford English Dictionary © 2008 Oxford University Press:
ringer/ˈrɪŋə(r)/

▶noun

• 1 informal an athlete or horse fraudulently substituted for another in a competition.

  ■ a highly proficient person brought in to supplement a team or group.

  ■ a motor vehicle whose identity has been fraudulently changed.

• 2 short for dead ringer.

• 3 a person or device that rings something.

• 4 Austral./NZ a shearer with the highest tally of sheep shorn.