An Etymological Dictionary of Astronomy and Astrophysics

1. Of or relating to → existence, especially  human existence.
   

2. Philo.:  Pertaining to what exists, and is thus known by experience rather  than reason; empirical as opposed to theoretical.
   

3. Logic: Denoting or relating to a → formula or → proposition asserting the
   existence of at least one object fulfilling a given condition; containing an → existential quantifier.
   

4. Of or relating to → existentialism (Dictionary.com).

Etymology (EN): From L.L. existentialis, → existence, → -al.

Etymology (PE): Hastiyâl, from hasti, → existence, + -al a suffix of attributes forming adjectives that often become nouns, in this case preferred to -i because hasti ends in -i, → -al.