Where does “экзистенциальный” come from?

экзистенциальный (Russian) comes from Late Latin existentialis, from Latin existentia, from Latin existens, from Latin existere, from Latin existo, from Latin ex, from Latin commūnicō, from Latin commūnis — whale, sea monster; abyss.

Ancestry of “экзистенциальный”, step by step

Step	Language	Word	Meaning
1	Late Latin	existentialis	—
2	Latin	existentia	existence
3	Latin	existens	Alternative form of exsistens
4	Latin	existere	present active infinitive of existō
5	Latin	existo	Alternative form of exsistō; to stand forth, come...
6	Latin	ex	A name of the letter "X"; out of, from
7	Latin	commūnicō	—
8	Latin	commūnis	—
9	Old Latin	com(m)oinis	—
10	Proto-Italic	kommoinis	—
11	Proto-Indo-European	ḱom-moy-ni-	held in common
12	Proto-Indo-European	ḱóm	beside, near, by, with
13	Proto-Indo-European	ḱe	Deictic particle, here; Post-positional...
14	Middle English	kyt	—
15	Russian	кит	whale; genitive plural of ки́та
16	Old Church Slavonic	китъ	whale
17	Ancient Greek	κῆτος	whale, sea monster; abyss

Every word from Ancient Greek κῆτος →