Chiefly Upper Southern U.S. Great: “ a powerful lot to say about faith and good works and free grace and preforeordestination, and I don't know what all” (Mark Twain)
adverb
Chiefly Upper Southern U.S.
Very: It was powerful humid.
derivatives
poẃer·ful·ly
adverb
poẃer·ful·ness
noun
The American Heritage® Dictionary of the English Language, Fourth Edition