An Etymological Dictionary of Astronomy and Astrophysics

1. A conventional or arbitrary mark, figure, or symbol used as an abbreviation for the word or words it represents. Related terms: → signal, → signature, → symbol, → index.
   

2. Math.: A plus sign or minus sign used as a symbol for indicating addition or subtraction; also a sign for indicating the positive or negative value of a quantity.
   

3. → sign of the zodiac.

Etymology (EN): M.E., from O.Fr. signe “sign, mark, signature,” from L. signum “mark, token, indication, symbol,” from PIE base *sek^w- “to see.”

Etymology (PE): Nešân “sign, mark,” from Mid.Pers. nišân “sign, mark, omen,” nišitan “to gaze, stare, look into,” niš in marv.niš “taking omen, foretelling, or divining from birds,” nišak “clear, evident,” from Proto-Iranian *niiaš- “to show,” from *ni- “down, below,” → ni- (PIE), + *iaš- “to show, appear;” cf. Armenian loanword niš “sign, mark, spot,” loaned also in Syriac as nyš “sign” (Cheung 2007).