An Etymological Dictionary of Astronomy and Astrophysics

1. Classical philosophy: That part of metaphysics which is concerned with the nature of existence or the essence of things.
   

2. Contemporary philosophy: The conceptions of existence in general, such as those dealt with in various versions of existentialism.
   

3. Informatics: A description of knowledge as a set of concepts within a domain and the relationships that can exist between those concepts. An ontology is designed for the purpose of enabling knowledge sharing and reuse.

Etymology (EN): From Mod.L. ontologia, from Gk. on (genitive ontos) “being” (pr.p. of einai “to be”), akin to L. esse “to be;” Pers. hastan, astan “to be,” hasti “existence, being,” as below; + -logia, → -logy.

Etymology (PE): Hasti-šenâsi, from hasti “existence,” from hastan “to be,” → entity, + -šenâsi, → -logy.