In the Islamic belief system, the opposite of Tawhīd is

The opposite of Tawhīd in the Islamic belief system is Shirk. Tawhīd is the fundamental belief in the oneness of God, and it is the most important concept in Islamic theology. It means that God is one, unique, and indivisible in His essence, attributes, and actions. Muslims believe that nothing and no one deserves worship or devotion except God. On the other hand, Shirk is the opposite of Tawhīd and refers to associating partners with God or attributing divine qualities to something or someone other than God. It is considered the greatest sin in Islam because it undermines the belief in the oneness of God and violates His rights as the only Creator, Sustainer, and Judge of the universe. Therefore, the answer to the question is Shirk.