ens or quod est (in philosophy, as translation of τό ὄν, ens, Quint.; quod est, Sen.): res (thing): essentia or substantia (in philosophy, as translation of οὐσία: first introduced by Cic., [according to Sen., Ep., 58, 4], and defended by Quint., 8, 3, 33, who refers ens, essentia to Sergius Flavius).