A little bit of History:
Monotheism is defined by the Encyclopædia Britannica as belief in the existence of one god or in the oneness of God.
The Oxford Dictionary of the Christian Church gives a more restricted definition: "belief in one personal and transcendent God", as opposed to polytheism and pantheism.
A distinction may be made between exclusive monotheism, and both inclusive monotheism and pluriform monotheism which, while recognising many distinct gods, postulate some underlying unity.
Monotheism characterizes the traditions of Atenism, the Bahá'í Faith, Cao Dai (Caodaiism), Cheondoism (Cheondogyo), Christianity, Deism, Eckankar, Islam, Judaism, Rastafarianism, Sikhism, Vaishnavism, Tenrikyo (Tenriism) and Zoroastrianism and elements of the belief are discernible in numerous other religions.