WordWeb Online

1. In contact with, on top of
   "the book upon the table";
   - on
    
2. Supported by
   "balanced upon one leg";
   - on
    
3. At or following a prescribed point in time
   "The contract was rendered void upon his death";
   - on

1. Being up to particular standard or level especially in being up to date in knowledge
   "up on the news";
   - abreast, au courant, au fait, apace [N. Amer]

See also: informed

Encyclopedia: Upon