Webster's Revised Unabridged Dictionary · 1913

Metamorphic

Metamorphic , adjective

[See Metamorphosis.]

1.
Subject to change; changeable; variable.
2.
Causing a change of structure.
3.
(Geology) Pertaining to, produced by, or exhibiting, certain changes which minerals or rocks may have undergone since their original deposition; -- especially applied to the recrystallization which sedimentary rocks have undergone through the influence of heat and pressure, after which they are called metamorphic rocks.