symbol

1. A material Object substituted for a moral or spiritual Truth... Used by the Greeks, much in the same way as we use the word "coupon," where one part corresponded with or represented another part. Hence, in language, the use of one thing to represent another; or, the use of a material object to represent a moral or spiritual truth. (Bullinger, 759)

1. Mysteerion means "secret;" and later it came to mean a "secret sign" or "symbol." Justin Martyr (A.D. 148) says that in all false religions the serpent was represented as "a great symbol and mystery."
Speaking of Isa. 7:14, "Behold, a virgin shall conceive and bear a son," he says "since this refers to the house of David, Isaiah has explained how that which was spoken by God to David, en mysteerio "in a mystery," would actually come to pass. Perhaps," he adds, "you are not aware, my friends, of this-that there were many sayings written epikealummenos "obscurely" or en parabolais "in parables;" or, mysteerios "in secret signs;" or en symbolois " in symbols;" which the prophets, who lived after the persons who said or did them, expounded." (Bullinger, 759)