ratio essendi
/ˈreɪʃɪəʊ ɛˈsɛndʌɪ/ /ˈrɑːtɪəʊ ɛˈsɛndi/Philosophy
noun
That by reason of which something exists.
Origin
Mid 19th century; earliest use found in William S. Hamilton (1788–1856), philosopher. From post-classical Latin ratio essendi from classical Latin ratiō + essendī, genitive of the gerund of esse to be.