(linguistics) One of fourteen Arabic letters that do not affect the pronunciation of the "L" of a preceding definite article (ال-). The "L" in the Arabic definite article is pronounced "L" when followed by a moon letter: e.g., القُرْآن. The fourteen moon letters are: ء, ب, ج, ح, خ, ع, غ, ف, ق, ك, م, ه, و, ي