Strong

The triliteral root qāf sīn wāw (ق س و) occurs in the Quran 7 times.

(2:74) Then your hearts became hardened after that, they became like stones or even harder (Arab. أَشَدُّ, ashaddu); but even from the stones there are rivers that burst forth, or from them are those that crack so that the water comes forth, or from them are what fall from the fear of God; God is not unaware of what you do.

Seven strongholds

(78:12) We constructed above you seven strongholds (Arab. شِدَادًا, shidādan)?