WordWeb Online

1. [informal] Very unpleasant
   "beastly weather";
   - hellish [informal], god-awful [informal], horrible [informal], hellacious [N. Amer, informal]
    
2. Resembling a beast; showing lack of human sensibility
   "beastly desires";
   - bestial, brute, brutish, brutal

1. In a beastly manner
   "she behaved beastly toward her mother-in-law"

Derived forms: beastlier, beastliest

See also: inhumane, unpleasant

Encyclopedia: Beastly