It has nothing to do with nuts. it means to summarize something in a short period of time.EX. "in a nutshell, I started the zombie appocalypse."
It means that it's the simplified version.
The image is of having just enough of something to fit into a nut shell. Figuratively, it means to give just the basics, only what is absolutely needed.
A nut is a hard-shelled dry fruit or seed with a separable rind or shell and interior kernel according to webster's
nut
The cashew nut
Walnut is an edible nut with a smooth thin shell.
Shell.
A coconut.
testicle
Cashew nut shell refers to the outer shell that encases the cashew nut, which is the seed of the cashew tree (Anacardium occidentale). This shell is not edible and contains toxic compounds, including anacardic acid, which can cause skin irritation. The shell is often processed to extract cashew nut shell liquid (CNSL), a valuable byproduct used in various industrial applications, such as in the production of resins, lubricants, and pesticides.
The best methods for cracking open a Brazil nut in its shell are using a nutcracker or a hammer to gently apply pressure until the shell cracks open. Be careful not to crush the nut inside while cracking the shell.
a doughnut because they are baked and dough nut that says it all that not shell but dough