i Register
In some senses, mightily is marked as literary, informal, obsolete. Watch for register when choosing this word.
adv
In a mighty manner.
The chivalrous knights entered the lists and fought mightily.
So cry Hand & Hyle the eldest of the fathers of Albions / Little-ones; to destroy the Divine Saviour: the Friend of Sinners. / Building Castles in desolated places, and strong Fortifications. / Soon Hand mightily devour'd & absorb'd Albions Twelve Sons.
In a mighty manner.
Sir, I ſhal not be ſlacke, in ſigne vvhereof / Pleaſe ye vve may contriue this afternoone, / And quaffe carovvſes to our Miſtreſſe health, / And do as aduerſaries do in lavv, / Striue mightily, but eate and drinke as friends.
But let man and beaſt be couered with ſackecloth, and cry mightily vnto God: yea, let them turne euery one from his euill way, and from the violence that is in their hands.
In a mighty manner.
[A]lthough he vvas a man mightely friended, yet vvas he by a publike decree baniſhed into one of the Abſyrtides, iſlan ds vpon the coaſt of Libvrnia.
Time, O mighty and mightily peopled city, / Time is busy with thee.
In a mighty manner.
He sounded mightily proud of himself.
Therein thou vvrong'ſt thy Children mightily.
In a mighty manner.
[T]his group of the lion and the man [a sculpture] now bear an unfinished, unwrought appearance, but you cannot look at it a moment, and not instantly avow the majesty and grandeur of the idea that once lay there so mightily embodied.
O, mightily seated and / Throned are our masters, / And steadily rooted; […]