This is the 697th most frequent Turkish word.
çelik
Steel.
Here, 'çelik' refers to the material 'steel'.
Bu bıçak çelikten yapılmıştır.
This knife is made of steel.
In this context, 'çelik' is used metaphorically to describe strength.
Çelik gibi güçlü bir iradeye sahip.
He/She has a will as strong as steel.
Here, 'çelik' is used to denote the industry related to steel.