'Differential diagnosis' definitions:

Definition of 'differential diagnosis'

noun

A systematic method of diagnosing a disorder (e.g., headache) that lacks unique symptoms or signs

From: GCIDE

Diagnosis \Di`ag*no"sis\, n.; pl. Diagnoses. [NL., fr. Gr. ?, fr. ? to distinguish; dia` through, asunder + ? to know. See Know.]
1. (Med.) The art or act of recognizing the presence of disease from its signs or symptoms, and deciding as to its character; also, the decision arrived at. [1913 Webster]
2. Hence, the act or process of identifying the nature or cause of some phenomenon, especially the abnormal behavior of an animal or artifactual device; as, diagnosis of a vibration in an automobile; diagnosis of the failure of a sales campaign; diagnosis of a computer malfunction. [PJC]
3. Scientific determination of any kind; the concise description of characterization of a species. [1913 Webster]
4. Critical perception or scrutiny; judgment based on such scrutiny; esp., perception of, or judgment concerning, motives and character. [1913 Webster]
The quick eye for effects, the clear diagnosis of men's minds, and the love of epigram. --Compton Reade. [1913 Webster]
My diagnosis of his character proved correct. --J. Payn. [1913 Webster]
Differential diagnosis (Med.), the determination of the distinguishing characteristics as between two similar diseases or conditions. [1913 Webster]