Shin is the thirteenth letter of the modern Arabic order and the twenty-first of the older abjad order, from which it takes the numeral value three hundred. It is the sin skeleton, three teeth running into a shallow bowl, carrying three dots above. It joins on both sides and keeps only its teeth and dots at the beginning and in the middle of a word. Its sound is the voiceless postalveolar sibilant, the sh of English.
Shin is a sun letter, and it is the letter from which the whole category takes its name. The Arabic word for sun begins with shin; the definite article before it is written al- and pronounced ash-, with the lam assimilated and the shin doubled; and the fourteen letters that behave this way have been called the sun letters ever since. The complementary set are the moon letters, named from the word for moon, which begins with qaf and keeps its lam.
Unlike sin, shin has a secure inherited name. It descends from the Northwest Semitic shin, whose sense has been reconstructed as a tooth, and it holds the numeral value three hundred in Arabic exactly as Hebrew shin does. Where the sibilants of the Semitic alphabets are otherwise difficult to align, shin is the fixed point that both its name and its value agree on. Its three dots make it one of only three Arabic letters pointed with three, alongside tha and the Persian and Urdu additions built on the same principle.