Wiktionary
mightly
a. 1 mighty; competent; capable; strong; powerful. 2 substantial; weighty; of import. 3 able; able to occur; possible. adv. 1 mightily. 2 very.
Usage examples of "mightly".
Get down them dancers, and don't you go for to forget that this litle pop o' mine is mightly liable to go off!