1. In a mighty manner; with might; with great earnestness; vigorously; powerfully.
Whereunto I also labor, striving according to his working, which worketh in me mightily. --Col. i. 29.
2. To a great degree; very much.
Practical jokes amused us mightily. --Hawthorne.
adv 1: powerfully or vigorously; "he strove mightily to achieve a
better position in life"
2: to a great degree; "rejoiced mightily at the news"