1620s, "of symptoms, relating to signs of diseases," from Latinized form of Greek sēmeiōtikos "significant, portending, worth marking," also "observant of signs," adjective form of sēmeiosis "indication," from sēmeioun "to signal, to interpret a sign," from sēmeion "a sign, mark, token," from sēma "sign" (see semantic). Its use in linguistics and psychology, "of or pertaining to the use of signs," is by 1923. Related: Semiotical (1580s).

1660s, in medicine, "branch of pathology concerned with the body's symptoms;" from semiotic; also see -ics. The meaning "study or doctrine of signs and symbols with special regard to function and origin" is by 1880. 

1690s, "sign language, the use of gestures to express thought," a sense now obsolete, from Greek sēmeion "a sign, mark, token," from sēma "sign, mark, token" (see semantic, and compare semiotic) + -ology. As "the branch of medical science concerned with morbid symptoms," 1839; as "logical theory of signs" by 1923. Related: Semiological.