'Metamorphism' definitions:

Definition of 'metamorphism'

(from WordNet)
noun
Change in the structure of rock by natural agencies such as pressure or heat or introduction of new chemical substances

Definition of 'Metamorphism'

From: GCIDE
  • Metamorphism \Met`a*mor"phism\, n. (Geol.) The state or quality of being metamorphic; the process by which the material of rock masses has been more or less recrystallized by heat, pressure, etc., as in the change of sedimentary limestone to marble. --Murchison. [1913 Webster]