thinker

noun4

1. •
   One who spends time thinking, contemplating or meditating.

   • The doer and the thinker No allowance for the other. — 1972
2. •
   An intellectual, such as a philosopher or theologian.
3. •
   (slang) A poser; a conundrum that requires some thinking.

   • HANK: The NRA is a Washington D.C. based organization. Are you telling me you support Washington D.C.? DALE: That's a thinker. — 1997
4. •
   (slang) The brain; the mind.

   • "Well, I tried to do like you and grandfather say; don't use my thinker, use imagination." — 2011