"scientific discrimination," especially in pathology, "the recognition of a disease from its symptoms," 1680s, medical Latin application of Greek diagnōsis "a discerning, distinguishing," from stem of diagignōskein "discern, distinguish," literally "to know thoroughly" or "know apart (from another)," from dia "between" (see dia-) + gignōskein "to learn, to come to know," from PIE root *gno- "to know."
"to ascertain or determine (a disease) from its symptoms," 1861, back-formation from diagnosis (q.v.) on the model of metamorphose, etc. Earlier was diagnosticate (by 1834). Related: Diagnosed; diagnosing.
1620s, "of or pertaining to diagnosis," also as a noun, "a symptom of value in diagnosis," from Greek diagnōstikos "able to distinguish," from diagnōstos, verbal adjective from diagignōskein "to discern, distinguish," literally "to know thoroughly" or "know apart (from another)," from dia "between" (see dia-) + gignōskein "to learn, to come to know," from PIE root *gno- "to know." Related: Diagnostics.
Although the work does not treat of the recent means of diagnosis—the thermometer, laryngoscope, cardiograph, etc.,—still it is complete as far as it goes. [book review in Medical Investigator, May 1867, p.94]
early 15c., percussioun, "a striking, a blow; internal injury, contusion," from Latin percussionem (nominative percussio) "a beating, striking; a beat as a measure of time," noun of action from past participle stem of percutere "to strike hard, beat, smite; strike through and through," from per "through" (from PIE root *per- (1) "forward," hence "through") + quatere "to strike, shake" (see quash).
In reference to musical instruments sounded by a stroke or blow, attested by 1776 (instrument of percussion). In medical diagnosis, "a method of striking or tapping the surface of the body to determine the condition of the organs in the region struck," by 1781.
The art of percussion, besides, although very simple in appearance, requires long practice, and a dexterity which few men can acquire. The slightest difference in the angle under which the fingers strike the thorax, may lead one to suspect a difference of sound which in reality does not exist. ["Laennec's New System of Diagnosis," in Quarterly Journal of Foreign Medicine and Surgery, November 1819]