It’s an adverb that can be
used in a
number of different ways:
1 It can mean particularly savage and violent;
2 It can mean in a direct and uncompromising way, where no attempt is made to disguise unpleasantness;
3 It can mean to an extremely unpleasant or harsh
degree;
1 He was brutally attacked in the
street;
2 It was a brutally
candid review of her performance;
3 The
thaw followed weeks of brutally cold weather;