A milquetoast is one who has a meek, timid nature. Yes, it is pronounced "milk-toast." Oxford Dictionaries indicates that it is the name of a 1930s cartoon character. Online Etymology indicates that it might be a form of milksop, a 14th century term for "an effeminite spiritless man," and also used as a reference to the infant Christ... literally a piece of bread soaking in milk, mild baby food.
This was not as nice as I would have thought. I'm pretty sure I saw this in either Wolf Hall or Bring Up the Bodies, Hilary Mantel's historical fiction novels about Thomas Cromwell... which means it is slightly anachronistic (unless Ms. Mantel used the word "milksop" instead). Nonetheless the term was used by Anne Boleyn's ladies in waiting to describe/deride the quiet Jane Seymour.