Mightily

He strove mightily to overcome his addiction to heroin.

Source: tatoeba (7774141)

"Well, my lad," he said, "and what is this great thing you have to tell me that is so mightily wonderful?"

Source: tatoeba (12428486)

In the wild countrey of the South, wherein the sunne beateth mightily upon the sandes, there liveth a people both ancient and wise, that feed upon divers creatures, such as the stranger would marvell at. For whereas our tables are garnished with bread, with fleshe, and with wine, their sustenance is found in the very bowels of the earth and in the flights of the aire. Chiefest among these meats is the Witchetty Grubbe, the fat larva of a moth, which hideth it selfe in the roote of the Acacia. With a staffe the women digge the grounde, and plucke forth this white worme of notable bignes. Some eat it raw, even then when it is taken from the roote, saying it hath the taste of almond or of the yolke of an egge. Others do cast it into the fire, so that the skinne is made crisp and the inside savoury, like unto the flesh of a bird well roasted. Thus doth the desert yeeld a dish both wholesome and strong. No lesse esteemed is the Honie Ant, whose belly is swolne with sweet licour, for shee serveth as a living vessel of nectar. The children plucke them gently from the earth, and at the biting of their bellies they finde a drinke more pleasant than the cuppe of grape. A small thing it is, yet of great delight.

Source: tatoeba (13414845)

The chivalrous knights entered the lists and fought mightily.

Source: wiktionary