The Collaborative International Dictionary of English v.0.48:
Instinctively \In*stinc"tive*ly\, adv. In an instinctive manner; by force of instinct; by natural impulse. [1913 Webster]WordNet (r) 3.0 (2006):
instinctively adv 1: as a matter of instinct; "he instinctively grabbed the knife"