A fallacy of ambiguity occurs whenever one uses a phrase that is unclear or when multiple definitions are used within a single argument. It takes the logical form of "Claim X is made; Y is concluded as a result of an unclear understanding of X." One example is "We have a good understanding of the world around us. Therefore, we know exactly how this world came to be." One thing does not necessarily lead to the other. I believe the answer would be an appeal to a lack of evidence.