Practice Essentials. The term âpernicious anemiaâ is an anachronismâit dates from the era when treatment had not yet been discovered, and the disease was fatalâbut it remains in use for megaloblastic anemia resulting from vitamin B12 deficiency due to lack of intrinsic factor (IF).
The definition of a fan is  a person who is very enthusiastic about someone or something, or a device that moves and cools the air. An example of a fan is a person who only wears gold and red in support of the San Francisco 49ers. An example of a fan is an electrical device with moving blades that cools air.
4. Fanboy. An extreme fan or follower of a particular medium or concept, whether it be sports, television, film directors, video games (the most common usage), etc. Known for a complete lack of objectivity in relation to their preferred focus. Usually argue with circular logic that they refuse to acknowledge.