adj. 25B6; adjective
a mighty blow : POWERFUL, forceful, violent, vigorous, hefty, thunderous.
a mighty warrior : FEARSOME, ferocious; big, tough, robust, muscular, strapping.
mighty industrial countries : DOMINANT, influential, strong, powerful, important, predominant.
mighty oak trees : HUGE, enormous, massive, gigantic, big, large, giant, colossal, mammoth, immense; informal monster, whopping (great), thumping (great), humongous, jumbo(-sized); Brit. informal whacking (great), ginormous.
feeble, puny, tiny.
25B6; adverb (N. Amer. informal) I'm mighty pleased to see you : EXTREMELY, exceedingly, enormously, immensely, tremendously, hugely, mightily, very (much); informal awfully, dreadfully, majorly, mega; Brit. informal well, jolly; N. Amer. informal plumb; informal, dated devilish, frightfully.