1. To a high degree or extent; favourably or with much respect
   "extremely interesting";
   - highly, majorly [informal]
    
2. To an extreme degree
   "extremely cold";
   - exceedingly, super, deathly, hella [US, informal], stone
    
3. To a great extent; over a large range or scale
   "salaries vary extremely";
   - enormously, exceedingly, terrifically [informal], tremendously, hugely, immensely, vastly, massively [informal], greatly

Encyclopedia: Extremely