on ‧ tol ‧ o ‧ gy /ɒnˈtɒlədʒi $ ɑːnˈtɑː-/ BrE AmE noun [uncountable]
[ Date: 1700-1800 ; Language: Modern Latin ; Origin: ontologia , from Greek ont- 'being' , from einai 'to be' ]
a subject of study in ↑ philosophy that is concerned with the nature of existence
—ontological /ˌɒntəˈlɒdʒɪk ə l◂ $ ˌɑːntəˈlɑː-/ adjective