E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The doctrine of the oneness of mind and matter, God and the universe. It ignores all that is supernatural, and the dualism of mind and matter, God and creation; and, as this is the case, of course, there can be no opposition between God and the world, as unity cannot be in opposition to itself. Monism teaches that all are but parts of one stupendous whole, whose body nature is, and God the soul; hence, whatever is, only conforms to the cosmical laws of the universal ALL.
Haeckel, of Jena, in 1866, revived this theory, and explains it thus: Monism (the correlative of Dualism) denotes a unitary conception, in opposition to a supernatural one. Mind can never exist without matter, nor matter without mind. As God is the same yesterday, to-day, and for ever, creation must be the same, or God would not be unchangeable.