This ivory disc formed the top/cap of a horn protector. See, for example, object 20.1455 for a full protector that employs an ivory cap such as this. Horn protectors were placed over the tips of animal horns (especially those of rams) to protect people from injury.
From Kerma, K1095x. March 1914: excavated by the Harvard University–Boston Museum of Fine Arts Expedition; assigned to the MFA in the division of finds by the government of Sudan; 1920: Received by the MFA. (Accession date: March 1, 1920)
Harvard University—Boston Museum of Fine Arts Expedition