From Wikipedia: "Risk aversion comes from a situation where a probability can be assigned to each possible outcome of a situation and it is defined by the preference between a risky alternative and its expected value." "Ambiguity aversion ... is defined through the preference between risky and ambiguous alternatives, after controlling for preferences over risk."
What is the preference between an ambiguous alternative and a certain outcome referred to? For example, the choice between a certain reward and an unknown probability to win a larger reward. I think it is not risk aversion, because an alternative's probability distribution of the outcomes is unknown, and not risk ambiguity because one alternative does not entail a risk.