(1) The nature of a disease; the identification of an illness. (2) A conclusion or decision reached by diagnosis. The diagnosis is rabies. (3) The identification of any problem. The diagnosis was a plugged IV. The word diagnosis comes directly from the Greek, but the meaning has been changed. To the Greeks a diagnosis meant specifically a "discrimination, a distinguishing, or a discerning between two possibilities." Today, in medicine that corresponds more closely to a differential diagnosis