Is a word denoting one of Allah's attributes, such as "Ar-Rahmah" (Mercy), considered uncreated as a name for the attribute, especially when the Prophet (peace be upon him) or one of creation describes Allah?

Mercy is a general attribute, and it is not intended to be an attribute of Allah except by attributing it to Him, in which case it is uncreated. As for the servant uttering and moving his tongue with the phrase "Allah's mercy," this is from his action, and the servant's action is created. So his voice and writing are created, but what is heard or written (Allah's mercy) is an attribute of Allah that is uncreated. An example of this is the saying of Imam Al-Bukhari: "You write: (Allah), so Allah in His essence is the Creator, and your handwriting is from your action, and it is created." Similarly, with the Noble Qur'an, the action of the reciter is created, but the pronounced and heard word is the uncreated speech of Allah.