Meaning

noun (computer science) a rigorous and exhaustive organization of some knowledge domain that is usually hierarchical and contains all the relevant entities and their relations

noun the metaphysical study of the nature of being and existence

originLearned borrowing from New Latin ontologia (1606, Ogdoas Scholastica, by Jacob Lorhard (Lorhardus)), from Ancient Greek ὤν, ὄντος (ṓn, óntos, “being”), present participle of εἰμί (eimí, “being, existing, essence”) + λόγος (lógos, “account”). By surface analysis, onto- + -logy. First known English use 1663: Archelogia philosophica nova; or, New principles of Philosophy. Containing Philosophy in…

Etymology from Wiktionary, CC BY-SA 3.0