WordWeb Online

1. In accordance with truth, fact or reality
   "she was now truly American";
   - genuinely, really, veritably
    
2. By right
   "baseball truly is the nation's pastime";
   - rightfully
    
3. With sincerity; without pretence
   "we are truly sorry for the inconvenience";
   - sincerely, unfeignedly
    
4. (used as an intensifier or sentence modifier) in fact
   "a truly awful book";
   - in truth, really

Antonym: insincerely

Encyclopedia: Truly, Madly, Deeply Vale