sigmoid

Reader's Digest ６月号のWord PowerクイズのテーマはThe Shape of Thingsで、私は１５問中６問も間違えましたが、６問の単語の内初めて見る単語は "sigmoid" だけでした。
答えは "curved like an S" で例文として "On Superman's chest sits a single bold, scarlet sigmoid symbol.が示されていました。
一応 "sigmoid" の説明を辞書でも確認します。
Merriam-Webster's Online Dictionary: 1 a: curved like the letter C; b: curved in two directions like the letter S
The shape sense of sigmoid is most often used in scientific contexts to describe an s-shaped curve on a graph. Usually, though, sigmoid is used in contexts relating to the sigmoid colon-the contracted and crooked part of the colon immediately above the rectum. Sigmoid comes from sigma, the name of the 18th letter of the Greek alphabet. At one time sigma had a common form that was shaped like the Roman letter C (hence sense 1a), but sigma is equivalent to the English letter S (hence sense 1b).