 Aristotle offers a test for ambiguity: try to construct a definition that encompasses both meanings and posit an ambiguity only if you fail. The notion of definition here has to be taken as a heavy-weight notion: ‘bank’ is ambiguous even though you can ‘define’ it as ‘financial institution or river side’. However, we can get a reasonable grip on what Aristotle had in mind. ‘Uncle’ is not ambiguous because it has a single definition that covers both: x is an uncle iff x is the brother of y and y has a child. 