Using your definition then, Social Security is not an entitlement program because those that receive payments from the system have paid money into the system. Its a rebate, right?
I doubt that S/S would qualify in the same way since there's no return of part of the payment in any direct way- and if then only many years later (or not at all) while the prebate is readily returned to the taxpayer. In addition, the S/S is conditioned upon wage income rather than any sort of tax payment - it's taken from the earner without recourse and not truly "paid by the taxpayer" as a tax. And not every taxpayer gets S/S - or has his income confiscated for it.
I've never seen any description of S/S calling it a rebate at all, but there is plenty of information that rightfully calls it an entitlement. The income tax amounts that some obtain on April 15 could be called a rebate, but if you can find a source calling S/S a rebate, I'd like to see it. So I very much disagree with your notion. In addition, it's a definition of the dictionary, not "mine".
Regardless of that, that's not what the thread is about in any event nor is whatever S/S might or might not be at all relevant to the FairTax but merely an attempted diversion..