A tax that increases in rate as the amount of money being taxed increases; for example, $20,000 is taxed at 5 percent, $20,001 to $45,000 is taxed at 10 percent, and so on. pro hac vice Latin. For this one purpose or occasion. The allowing of something not usually allowed, usually promissory note referring to an attorney who normally could not practice in a certain jurisdiction, but is allowed to just for one case