Monism

Etymology

From Greek "monos," "single, alone." The term was coined by the philosopher Christian Wolff in the 1700s. Its classic modern expression is Baruch Spinoza’s claim that there exists only one substance — which he called God or Nature — of which everything else is an aspect.

noun · /MOH-niz-um/
The view that reality is ultimately made of one kind of thing or is a single unified whole, rather than divided into fundamentally different substances.
What it names
A handle for the drive to unify — the conviction that beneath apparent divisions of mind and matter, or of many things, there is really one underlying reality.
Example
Her monism was almost mystical: mind and matter, she insisted, were just two faces of one underlying reality.
Related idea
Dualism is the direct rival, splitting reality into two irreducible kinds of thing; monism dissolves that split into one.