diagnosis: [17] The underlying meaning of Greek diágnōsis was ‘knowing apart’. It was derived from diagignóskein ‘distinguish, discern’, a compound verb formed from the prefix dia- ‘apart’ and gignóskein ‘know, perceive’ (a relative of English know): In postclassical times the general notion of ‘distinguishing’ or ‘discerning’ was applied specifically to medical examination in order to determine the nature of a disease. => know
1680s, medical Latin application of Greek diagnosis "a discerning, distinguishing," from stem of diagignoskein "discern, distinguish," literally "to know thoroughly," from dia- "apart" (see dia-) + gignoskein "to learn" (see gnostic).
