1. Having or capable of exerting power.
2. Effective or potent: a powerful drug.
3. Chiefly Upper Southern US Great: "[Everybody had] a powerful lot to say about faith and good works and free grace ... and I don't know what all" (Mark Twain).
Chiefly Upper Southern US
Very: It was powerful humid.
Our Living Language In the Upper Southern United States the words powerful and mighty are intensives used frequently in the same way as very: Your boy's grown powerful big. The new baby is mighty purty. Powerful is used as an adjective in some expressions: The storm did a powerful lot of harm. In the same dialect region the noun power has, in addition to its standard meaning, the sense of "a large number or amount." This sense appears in the Oxford English Dictionary as common in dialectal British English of the 1700s and 1800s: "It has done a power of work" (Charles Dickens). All these derivative senses of power and might take advantage of the notion of strength inherent in these nouns, making them natural intensives.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.