ص ل دṣ-l-d
(ن) صَلَدَ يَصْلُدُ صُلُوْدًاṣalada yaṣludu ṣulūdan: to be hard and smooth, such that nothing stays on it.
صَلْدٌṣald: a hard smooth rock on which no soil settles. Only once in the Quran, and that in the parable of the hypocrite's charity: ﴿فَاَصَابَهُۥ وَابِلٌ فَتَرَكَهُۥ صَلْدًا﴾ (Al-Baqarah 2:264) — i.e. the rain washed away the soil and the rock was left bare.