To put it slightly differently, uncertainty is a type of ambiguity where the probability of an act or outcome cannot be calculated whereas a risk has some element of calculation - there is a certain probability of some known act or outcome occurring.
2  BIS Review 58/2007  •  Improved market liquidity, reflecting a host of different factors, such as development of market infrastructure, broadening of investor base, and more prudent macroeconomic policies in many emerging market countries, has reduced liquidity risk premia.