adv. [ From Mighty. ] 1. In a mighty manner; with might; with great earnestness; vigorously; powerfully. [ 1913 Webster ]
Whereunto I also labor, striving according to his working, which worketh in me mightily. Col. i. 29. [ 1913 Webster ]
2. To a great degree; very much. [ 1913 Webster ]
Practical jokes amused us mightily. Hawthorne. [ 1913 Webster ]