'in a nutshell' definitions:

Definition of 'in a nutshell'

adverb

Summed up briefly; "gave the facts in a nutshell"; "just tell me the story in a nutshell"; "explained the situation in a nutshell"

From: GCIDE

Nutshell \Nut"shell`\, n.
1. The shell or hard external covering in which the kernel of a nut is inclosed. [1913 Webster]
2. Hence, a thing of little compass, or of little value. [1913 Webster]
3. (Zool.) A shell of the genus Nucula. [1913 Webster]
in a nutshell in a summarized and very abbreviated form; -- of statments, descriptions, reports, and other communications; as, to describe the convention in a nutshell.
To be in a nutshell or To lie in a nutshell,, to be within a small compass; to admit of very brief or simple determination or statement. "The remedy lay in a nutshell." --Macaulay. [1913 Webster +PJC]