1) Medical specialty 2) Medicine 3) Nosology 1) Nosology 
• (n.) That part of medicine which has to do with ascertaining the nature of diseases by means of their symptoms or signs.
(di″әg-nos´tiks) the science and practice of diagnosis of disease.
Di`ag·nos'tics noun That part of medicine which has to do with ascertaining the nature of diseases by means of their symptoms or signs. « His rare skill in diagnostics .» Macaulay. 
diagnostics 1. The art of identifying illnesses or disorders in patients through diagnosis or procedures for diagnosis; takes a singular verb. 2. That part of medicine which has to do with ascertaining the nature of diseases by means of their symptoms or signs.
the discipline or practice of diagnosis.