marker

Concise Oxford English Dictionary © 2008 Oxford University Press:
marker/ˈmɑːkə(r)/

▶noun

• 1 an object used to indicate a position, place, or route.

  ■ a distinctive feature or characteristic indicative of a particular quality or condition.

  ■ Genetics an allele used to identify a chromosome or to locate other genes on a genetic map.

• 2 a felt-tip pen with a broad tip.

• 3 Brit. (in team games) a player who marks an opponent.

• 4 a person who marks a test or examination.

  ■ a person who records the score in a game, especially in snooker or billiards.

• 5 N. Amer. informal a promissory note; an IOU.