brainlet

noun4

1. •
   (informal) A small brain; the brain of someone or something small or of someone who is not very intelligent.

   • But a shade of bygone sorrow, Like a dream upon the morrow, Round his tiny brainlet clinging, Sets the wee cock ever singing, — 1884
2. •
   A dolt; a fool; someone having a small brain.

   • I think he told Claudine the same thing when they met, and convinced the tiny brainlet of his sincerity. — 1905
3. •
   A subcomponent of a brain or thinking system.

   • Let's call these five smaller brain units, brainlets: […] Each brainlet is found in a specific part of your thinking brain. — 2008
4. •
   (no longer used) The cerebellum.