\Im`ma*te"ri*al*ism\, n. [Cf. F.
immat['e]rialisme.]
1. The doctrine that immaterial substances or spiritual being
   exist, or are possible.
2. (Philos.) The doctrine that external bodies may be reduced
   to mind and ideas in a mind; any doctrine opposed to
   materialism or phenomenalism, esp. a system that maintains
   the immateriality of the soul; idealism; esp., Bishop
   Berkeley's theory of idealism.