ens per accidens /enz pər akˈsi-dənz or per a-ki-dānsˈ/ noun

(in Aristotelian philosophy) that which exists only as an accident of a substance (an ens per se /sē or sā/)

ens rationis /rā-shi-ōˈnis or ra-ti-ōˈ/ noun

An entity of reason, existing purely in the mind opposed to ens reale /rē-āˈlē or re-äˈle/ which exists actually or potentially outside the mind