1.  existential(s = adj.all) experiential - derived from experience or the experience of existence; "the rich experiential content of the teachings of the older philosophers"; "formal logicians are not concerned with existential matters"

2.  existential(a = adj.pert) - of or as conceived by existentialism; "an existential moment of choice"

3.  existential(a = adj.pert) - relating to or dealing with existence (especially with human existence);
Derived form noun existence₁

1.  Having existence. [1913 Webster]

2.  of or pertaining to, or having the character of, existentialism. [PJC]

3.  specifying actual existence, rather than only possibility; as, the existential operator. [PJC]
"Existentially as well as essentially intelligent." [1913 Webster]

existential, adj.
1 of or relating to existence.
2 Logic (of a proposition etc.) affirming or implying the existence of a thing.
3 Philos. concerned with existence, esp. with human existence as viewed by existentialism.

Derivative:
existentially adv.

Etymology:
LL existentialis (as EXISTENCE)

existential operator, existential philosophy, existential quantifier