Gist

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Gist, etymology

Gist in english means "the main point". 

It was new to me that gist, curiously also means to summarise: 

1. 1991

   He put a manila folder on the DA's desk. The DA looked at them blearily. ‘You want to gist them for me?’

   C. Buckley, Wet Work i. v. 42

....and in Nigerian English to chat: 

1. 1992

   It was..one of those lazy afternoons, and we were all—us children, that is—gisting outside.

   M. E. Ezekiel, Windsongs 5

Gist has a fascinating etymology from jacere (Latin) meaning to throw, hurl or cast to gésir (Old French) meaning to lie. So we have this idea of something being thrown and then something lying on the ground.  Apparently gésir, which is still used today, but not so often, has a sense of illness or death, which coming from its root of being hurled is not altogether surprising.  

I rather like the idea that idea that once something has settled into a restful state, the main point (possibly that it is dead or very sick) emerges but that could be a stretch of interpretation.

The headline image indicates it enters English as a legal term meaning "gives grounds to proceed". The eighteenth century has several uses of gist in a legal context:

1769

These charges..are the points and very gist of the indictment.

W. Blackstone, Commentaries on Laws of England vol. IV. 333
1. 1791

   This is the great gist of the charge against him.

   E. Burke, Appeal New to Old Whigs 30
2. 1835

   The gist of the action being the assault and battery.

   P. Bingham, New Cases Court Common Pleas vol. 1 72

So gist grounds becomes "grounds" retaining the idea of "the main reason" (for proceeding).  

From here it loses the legal sense and becomes simply "the main point or essence". 

By 1820 it is closer to our current meaning, "The substance or pith of a matter, the essence or main part."

I always thought it also meant "the rough idea" but this nuance is not in the OED.   People say - you get the gist meaning you get the general picture, if not all the details.  

“Gist, N. Various sensse.” Oxford English Dictionary, Oxford UP, September 2023,