Essence
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
That which is indispensable to that of which it is the essence.
— Essence of the contract. Any condition or stipulation in a contract which is mutually understood and agreed by the parties to be of such vital importance that a sufficient performance of the contract cannot be had without exact compliance with it is said to be "of the essence of the contract."