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. (Odysseus); note the two sigmas in the center of the name, and the word-final sigma at the end.