Polytheism involves belief in multiple deities. The existence of several gods does not by itself settle their relationships, moral authority, or the forms of devotion directed toward them.
Monotheism and religious dualism concern different questions about ultimate reality. The presence of an adversary does not automatically establish two equal divine principles.
Religious syncretism concerns the combination of ideas, figures, and practices from different traditions. Similarity of names or imagery alone does not establish identity or historical continuity.