n.1 a stone, post, etc., used to mark a position, place reached, etc.
2 a person or thing that marks.
3 a felt-tipped pen with a broad tip.
4 a person who records a score, esp. in billiards.
5 a flare etc. used to direct a pilot to a target.
6 a bookmark.
7 US sl. a promissory note; an IOU.