What is the definition or description of: diagnosis?

Cause of something: It is the cause of something. For example a large cavity could be the cause of a toothache and the diagnosis would be a cavity or caries.

Diagnosis: Constellation of signs, symptoms & findings that support a label for an illness. It identifies the nature & causes of an illness. Medical diagnosis is a cognitive process, where the physician uses several data sources & puts the pieces of the puzzle together to formulate a tentative diagnosis.