Polytheism
Polytheism is belief in, or worship of, multiple gods or divinities. The word comes from the Greek words poly+theoi, literally "many gods." Most ancient religions were polytheistic, holding to pantheons of traditional deities, often accumulated over centuries of cultural interchange and experience. Present-day polytheistic religions include Hinduism, Shinto, some forms of Wicca, Vodun, and Asatru. Buddhism is regarded by some non-practitioners as polytheistic although this view of the religion is rejected by most adherents. Some Jewish and Islamic scholars regard the Christian doctrine of the Trinity as bordering on polytheism, a view that Christians strongly reject.
However, there are some serious philosophical problems when thinking about the definition of God in relation to polytheistic beliefs. By the broadest definition in most dictionaries, God refers to the supreme being that is above everything else. By very definition, this requires that it be only One being. The reasoning is that if this being was just another one of many gods, He would not necessarily be the highest or supreme. A polytheist might reply that there is one highest God with multiple lesser gods (i.e. Henotheism). However, this is still in contrast to the definition because those lesser beings cannot be referred to as "God", simply because they are not the supreme being. The definition of a supreme God demands that He is One.