In a nutshell

To put something in the casing of a nut would be to confine it in a very small space. The origin is Shakespeare Hamlet Act II, Scene II, “O God! I could be bounded in a nutshell and count myself a king of infinite space, were it not that I have bad dreams.” This Shakespearean use is literal and refers to physical space whereas the OED maintains the figurative meaning of in a nutshell, meaning in few words, dates from the early 19th century c. 1831.