spiritualist

Concise Oxford English Dictionary © 2008 Oxford University Press:
spiritualism/ˈspɪrɪtʃuəlɪzəm/

▶noun

• 1 a system of belief or religious practice based on supposed communication with the spirits of the dead, especially through mediums.

• 2 Philosophy the doctrine that the spirit exists as distinct from matter, or that spirit is the only reality.

– derivatives
spiritualist noun,
spiritualistic adjective.