c.1200, nute-scalen; see nut + shell (n.). Figurative use with reference to "great condensation" (1570s) supposedly originally is a reference to a copy of the "Iliad," mentioned by Pliny, which was so small it could fit into the shell of a nut.
To condense; sum up: If I'm forced to nutshell it, the show is about community, it's about the workplace and the town
[1883+; fr the idiom put something in a nutshell]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with in a nutshell
Concisely, in a few words, as in Here's our proposal—in a nutshell, we want to sell the business to you. This hyperbolic expression alludes to the Roman writer Pliny's description of Homer's Iliad being copied in so tiny a hand that it could fit in a nutshell. For a time it referred to anything compressed, but from the 1500s on it referred mainly to written or spoken words.