Definition of "thinker"

thinker

/ˈθɪŋ.kə(ɹ)/

noun
plural thinkers
1. One who spends time thinking, contemplating or meditating.
  Quotations
  The doer and the thinkerNo allowance for the other.
  1972, “Thick As A Brick”, Ian Anderson (lyrics), performed by Jethro Tull
2. An intellectual, such as a philosopher or theologian.
3. (slang) The brain; the mind.
  Quotations
  "Well, I tried to do like you and grandfather say; don't use my thinker, use imagination."
  2011, Arthur Kornhaber, Rosie's Miracle: A Novel, page 271
4. (slang) A poser; a conundrum that requires some thinking.
  Quotations
  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, "How to Fire a Rifle Without Really Trying" (King of the Hill TV series, season 2 episode 1)