1) Alphabetic character 2) Letter 3) Letter of the alphabet 
Samekh or Simketh is the fifteenth letter in many Semitic alphabets, including Phoenician, Hebrew, and Aramaic, representing /s/. The Arabic alphabet, however, uses a letter based on Phoenician šin to represent /s/ (see there); however, that glyph takes Samekh`s place in the traditional Abjadi order of the Arabic alphabet. The Phoenician letter ....
[n] - the 15th letter of the Hebrew alphabet
noun the 15th letter of the Hebrew alphabet