term:

Gist

gist n

[Anglo-French, in the phrase laccion gist the action lies or is based (on), from gisir to lie (of process), from Old French gesir to lie, ultimately from Latin jacere]
: the ground or foundation of a legal action without which it would not be sustainable

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.