semiology n.

"relating to significance or meaning," 1894, from French sémantique, applied by Michel Bréal (1883) to the psychology of language, from Greek sēmantikos "significant," from sēmainein "to show by sign, signify, point out, indicate by a sign," from sēma "sign, mark, token; omen, portent; constellation; grave" (Doric sama), from PIE root *dheie- "to see, look" (source also of Sanskrit dhyati "he meditates;" see zen).

The word has tended to become loose in application. Semanticize "invest (something) with meaning; analyze semantically" is by 1942.

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).

word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.

The second element is prop[erly] -logy (-logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary]