Spiritualism is the belief that the dead are still there in some form and can pass messages to the living, usually through a person called a medium. It is a specific thing, not a vague feeling: it grew into an organised movement in the 1800s in America and Britain, with meetings called séances, sitting round tables in the dark, tapping sounds, and people who claimed to speak with a voice not their own. It had a large following, especially after wars, when huge numbers of grieving families wanted one more word with someone they had lost. Spiritualist churches still exist today and hold services. That history is why the word tends to carry a tone — depending on who says it, it sounds either sincere and comforting or like something exposed long ago as a trick. A second, much rarer use appears in philosophy books, where spiritualism means the view that spirit or mind is the real basis of the world, opposite to materialism; you will only meet that use in academic writing. A person who follows it is a spiritualist; the adjective is spiritualist too.