According to academic theorist Michel Foucault, the characteristics of a discipline are: shared discourse and shared epistemology. Shared discourse means that all individuals within the discipline share basic assumptions as to what constitutes the discipline.
Usually, this is pretty self-evident. All biologists share a notion of what biology is and what topics fall within it. However in some disciplines the line is more blurred. For example, in the discipline of theology, there are questions as to what phenomena ought to be included in the discipline. Should the study of miracles or personal revelations be included as legitimate aspects of the discipline, or no?
Nursing seems to meet the criterion of shared discourse, as most individuals participating in the discipline share a notion of what nursing is.
Shared epistemology means that individuals within the discipline have an agreement about how knowledge is constructed or obtained. Scientists' agreement is to how knowledge is obtained has been codified as the scientific method. Sociologists, psychologists, anthropologists etc. use discipline-specific methods and processes to create new knowledge within their discourse. Nursing contains within it the epistemological assumptions of bio-medicine, and thus does have a shared, albeit derivative epistemology.
Nursing meets the two basic criteria for a discipline: shared discourse and shared epistemology.