This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

ad. In a manner that one does not believe.

ad. To an extent not to be believed.

ad. Contrary to expectations, amazingly.

ad. in an unbelievable manner

ad. not easy to believe

"And now, even more unbelievably, is this secret plan of China to take over America according to O'Donnell."

conceivably    irretrievably