noun

• (geology) The process by which rocks are changed into other forms by the application of heat and/or pressure.
  "burial means that the ambient pressure on the rock increases – as does the temperature. This encourages metamorphism."
• (zoology) The process by which insects develop through life stages, for example, those of embryo, larva, pupa and imago. The life cycle of the butterfly is one of complete metamorphosis, in which the embryo grows within the egg, hatches into the larval stage caterpillar, enters the pupal stage within its chrysalis, and finally emerges as an adult butterfly imago.
• (by extension) Any dramatic change from one thing to another
  "December 28 2015, Barrett Pall writing in the Huffington Post, 11 Reasons Why You Shouldn’t Be Happy Ultimately, being happy means that even when things aren’t perfect you still understand how blessed you truly are. You remain in a constant state of uncomfortable change, evolution and metamorphism because you know that this is a process that requires care and love."