Simple past tense and past participle of thwack.(verb)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "thwacked" in a sentence
"He had to commit everything to that, but he made the full commitment, and the sword thwacked home against Ledales torso with an impact that made him grunt in pain."
"The recent nose dive in crude-oil prices could provide some much-desired relief to shipping companies, airlines and other industries thwacked this year by soaring energy costs, but it will likely take longer to see an impact on their customers' wallets."
"How about video of the owie he suffered when he thwacked his head on the backboard on an alley-oop late in the Los Angeles Clippers' 98-90 victory over Minnesota?"