WordWeb Online

1. To certain extent or degree
   "he is fairly clever with computers";
   - reasonably, moderately, pretty [informal], jolly [Brit, informal], somewhat, middling, passably, middlingly, averagely
    
2. Without favouring one party, in a fair evenhanded manner
   "deal fairly with one another";
   - fair, evenhandedly
    
3. In conformity with the rules or laws and without fraud or cheating
   "they played fairly";
   - fair, clean

Antonym: below the belt

Encyclopedia: Fairly