from The Century Dictionary.
- noun In Greek antiquity, a device or badge, corresponding to the crest of later times, as that borne on the shield of a soldier, or that chosen as its distinguishing mark by a city, etc.
- noun In the Greek alphabet, one of three obsolete letters used only as numerals.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun an insignia or some other distinguishing symbol
- noun another name for the Greek letter
- noun a term for the
digamma, koppa, or sampias a Greek numeral sign
from Wiktionary, Creative Commons Attribution/Share-Alike License
 That is, the letters z, x, ps all contain s, whose value is six, and which was called episemon by the Greeks.
 The old Latin version renders episemon, insigne, illustrious, but there seems to be a reference to the Valentinian notion of the mystic number of 888 formed (10+8+200+70+400+200) by the numerical value of the letters in the word 'Iesous.
Even numbers are female, odd numbers male, by the union of the first of these, 2 3, was begotten the episemon, or 6, the number of our Salvation.
The 6 is purposely omitted for it is the episemon and not a letter of the usual Greek alphabet.
The episemon, or 6, is a number full of potency; the name Iesous consists of six letters, hence the name of the Saviour.