from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Slang Used as an intensive: You've done a heckuva good job.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Heck of a; extreme;
Alteration of heck of a.(American Heritage® Dictionary of the English Language, Fourth Edition)
Written form of a reduction of "Heck of a" (Wiktionary)