|a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.|
|a chattering or flighty, light-headed person.|
|informal having or having scored an advantage or lead over someone or something|
Having an advantage or lead over someone, as in Sara is one up on Jane because she passed algebra in summer school. This expression comes from sports, where it means to be one point ahead of one's opponents. It was transferred to more general use about 1920.