<p>The creation of natural definitions is a phase of any methodology to build formal ontologies. In order to reach formal definitions, one should first create natural language definitions according to sound principles. We gather a set of principles available in literature and organize them in a list of stages that one can use to create good definitions in natural language. In order to test the set of principles, we conducted a case study in which we create definitions in the domain of cancer, more specifically, definitions for acute myeloid leukemia. After creating and validating the definition of this specific kind of leukemia, we offer remarks about the experiment.</p>