σημεῖον
Alt. σημεῖον, ου, τό,
Etym. σῆμα
I. "a sign, a mark, token", Hdt., attic
2. "a sign from the gods, an omen", Soph., Plat.: esp. of "the constellations", Eur.
3. "a sign or signal" to do a thing made by flags, Hdt.; αἴρειν, κατασπᾶν τὸ ς. to make or take down "the signal for battle", Thuc.; τὰ σημεῖα ἤρθη "the signals agreed upon" were made, id=Thuc.
4. "an ensign or flag", on the admiral's ship, Hdt.; on the general's tent, Xen.:—then, generally, "a standard, ensign", Eur.: hence, "a boundary, limit", Dem.
5. "a device" upon a shield, Hdt., Eur.; upon ships, "a figure-head", Ar.
6. "a signal, watchword", Thuc.
II. in reasoning, "a sign or proof", Ar., Thuc., etc.:— σημεῖον δέ: or σημεῖον γάρ: (to introduce an argument) this is "a proof" of it, Dem., etc.