What's the difference between diaeresis and metaplasm?

Diaeresis

Definition:

• (n.) Alt. of Dieresis

Example Sentences:

• (1) (That's why we all love the New Yorker's fanatical devotion to the diaeresis.)

Metaplasm

Definition:

• (n.) A change in the letters or syllables of a word.

Example Sentences: