Oleaster \O`le*as"ter\, n. [L., fr. olea olive tree. See {Olive}, {Oil}.] (Bot.) (a) The wild olive tree ({Olea Europea}, var. sylvestris). (b) Any species of the genus {El[ae]agus}. See {Eleagnus}. The small silvery berries of the common species ({El[ae]agnus hortensis}) are called {Trebizond dates}, and are made into cakes by the Arabs.