What is the linguistic meaning of "bukm"?

Imām Ibn al-Jawzī (d. 597 AH / 1201 CE) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. People who are mute, unable to speak. [Muqātil, Abū ʿUbayd, and Ibn Fāris]
2. Bakam (the verbal noun) means a defect in the tongue that prevents speech (rather than complete muteness). It has also been suggested: muteness is a result of this defect. [Mentioned by ʿAlī ibn ʿUbayd Allāh]
3. It means a defect in the heart that prevents one from comprehending and understanding anything. Thus they were corrupt in their ability both to understand and to speak. [Mentioned by ʿAlī ibn ʿUbayd Allāh]