«وَقَمَرُهَا كَتَعْوِيذٍ مِنْ لُجَيْنٍ»
Its moon resembled a small amulet made of silver.
Lujayn means silver, while taʿwīdh supplies the image of a small suspended ornament or amulet. The small, gleaming moon is compared with a silver object.
The particle ka- marks an explicit comparison. This simile follows the more metaphorical image of the night wearing a two-coloured skin.