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1. To a massive degree or in a massive manner
   "tonight the haddock were shoaling massively in three hundred fathoms"
    
2. [informal] Used as an intensifier
   - very, really, real [N. Amer], rattling [informal], mucho [informal], thoroughly, cracking [Brit, informal], rotten [informal], dirty [Brit, informal], excellently, magnificently, splendidly, famously, tremendously [informal], capitally, awesomely [informal]
    
3. [informal] To a great extent; over a large range or scale
   "salaries vary massively";
   - enormously, terrifically [informal], tremendously, hugely, immensely, vastly, greatly

Encyclopedia: Massively