Sigma
Sigma (upper-case Σ, lower-case σ, lower-case in word-final position ς; Greek σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. When used at the end of a word, when 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.
History
The shape and alphabetic position of Sigma is derived from Phoenician shin 𐤔 
.
Etymology
The name of sigma, according to one hypothesis, may continue that of Phoenician Samekh. According to a different theory, its original name may have been "San" (the name today associated with another, obsolete letter), while "sigma" was a Greek innovation that simply meant "hissing", based on a nominalization of a verb σίζω (sízō, from earlier *sig-jō, meaning 'I hiss').
Uppercase of esh
The uppercase form of sigma was re-borrowed into the Latin alphabet to serve as the uppercase of modern esh (lowercase: ʃ).
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