This is the 12347th most frequent Russian word.
каменный
"Каменный" means "stone" or "made of stone" in English.
In this sentence, 'каменная' as an adjective describes the wall as being made of stone, denoting its material composition.
Старая каменная стена окружала древний замок.
The old stone wall surrounded the ancient castle.
Here, 'каменным' metaphorically describes a facial expression as unchanging and emotionless, conjuring an image of physical rigidity.
Её лицо оставалось каменным, несмотря на все усилия его рассмешить.
Her face remained stone-like despite all efforts to make her laugh.
In this instance, 'каменной' metaphorically suggests a sensation of heaviness or numbness, likening the leg to the rigidity or weight of stone.