Monism stands against dualism and pluralism. It takes many forms: material monism, idealist monism, Spinoza’s one substance, the neutral monism of William James and Bertrand Russell. Advaita Vedānta is often called monistic, though its own word is non-dual, which denies a second without asserting a countable one.
Monism
The view that reality is ultimately one, whether one substance, one kind of thing or one principle.