Translation of "sun letter" into French

One of fourteen Arabic letters that cause the "L" of a preceding definite article to be assimilated in pronunciation. The sun letter suppresses the sound of the "L" and then geminates: al + ṣīn = aṣ-ṣīn. The effect of the sun letter is limited to pronunciation and does not affect the spelling: الصّين. The fourteen sun letters are: [..]