pathognomy
/pəˈθɒɡnəmi/noun
1Knowledge or study of the passions or emotions, especially the facial expression of them.
2The knowledge or study of the signs and symptoms by which diseases may be distinguished; a description of such signs and symptoms. rare.
Origin
Late 18th century; earliest use found in Thomas Holcroft (1745–1809), writer. From patho- + -gnomy, after pathognomic.