Read the dictionary definition of mightily. All definitions for this word.
1. (Southern regional intensive) very; to a great degree
1. the baby is mighty cute
2. he's mighty tired
3. it is powerful humid
4. that boy is powerful big now
5. they have a right nice place
6. they rejoiced mightily
2. powerfully or vigorously
1. he strove mightily to achieve a better position in life