Use an English dictionary.
: of, relating to, constituting, or providing an instance *empirical laws for which there is instantial evidence— Arthur Pap*
Of or pertaining to an instance or instances; furnishing an instance.
-This entirely distinct and peculiar use of the term ‘existential’ has given rise to endless confusion; and‥the term should be entirely discarded and replaced by some such term as instantial, or, more accurately, indeterminately instantial.(1922 W. E. Johnson Logic II.)