brainlet

/B R EY1 N L AH0 T/
noun
  1. 1

    (informal) A small brain; the brain of someone or something small or of someone who is not very intelligent.

  2. 2

    (by extension) A dolt; a fool; someone having a small brain.

  3. 3

    A subcomponent of a brain or thinking system.

  4. 4

    (obsolete) The cerebellum.