Sigma (upper case Σ, lower case σ; Greek Σιγμα, lower case in word-final position ς) is the eighteenth letter of the Greek alphabet, and carries the /s/ sound. In the system of Greek numerals it has a value of 200. When used at the end of a word, and the word is not all upper case, the final form (ς) is used. (e.g. Ὀδυσσεύς (Odysseus) - Note the two sigmas in the center of the name, and the word-final sigma at the end.) It is not to be confused with the cedilla ç. The letter is ultimately derived from Phoenician Šin 𐤔. However, its name derives from Samekh. The uppercase form of sigma was borrowed into the Latin alphabet to serve as the uppercase of esh (lowercase: ʃ). Disigma, or \"double sigma\", is a non-current term for the character Sampi. 
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