What is the root of the word miracle?

Luke 23:8 - Now when Herod saw Jesus, he was exceedingly glad; for he had desired for a long time to see Him, because he had heard many things about Him, and he hoped to see some miracle done by Him. The Word translated "miracle" is the Greek "semeion," which means "a sign, mark, token; an unusual occurence, transcending the common course of nature."