1615–20;(def 3) < Greeksēmeiōtikós significant, equivalent to sēmeiō-, verbid stem of sēmeioûn to interpret as a sign (derivative of Greeksēmeîon sign) + -tikos-tic; (def 4) < Greeksēmeiōtikḗ, noun use of feminine of sēmeiōtikós, adapted by John Locke (on the model of Greeklogikḗlogic, etc.; see -ic) to mean “the doctrine of signs”; (defs 1, 2) based on Locke's coinage or a reanalysis of the Gk word
1620s, "of symptoms, relating to signs of diseases," from Greek semeiotikos "significant," also "observant of signs," adjective form of semeiosis "indication," from semeioun "to signal, to interpret a sign," from semeion "a sign, mark, token," from sema "sign" (see semantic). Its use in psychology dates to 1923. Related: Semiotical (1580s).