break the buck

break the buck
 v. phr.— «He thinks it’s unlikely the companies running money market funds would allow them to “break the buck,” as it’s known in Wall Street parlance even if the funds lost money on SIV-related investments. The draw of money market funds, of course, is that an investor putting in $1 get $1 back plus interest. If a fund were to, say, give back only 90 cents for every dollar, investors would be outraged.» —“Money Market Investors Face Latest Worry” by Tim Paradis Forbes Oct. 23, 2007. (source: Double-Tongued Dictionary)