This is the 794th most frequent Turkish word.
demir
Iron.
In this sentence, 'demir' is used as an adjective, modifying the noun 'kapı' (door) to specify the material it is made of.
Demir kapıyı açarak odaya girdi.
He entered the room by opening the iron door.
Here, 'demir' functions as a noun, referring to the chemical element or mineral.
Demir, insan vücudu için önemli bir mineraldir.
Iron is an important mineral for the human body.
In this case, 'demir' is used as a noun, and it describes the substance contained in the pills.