Smith's Bible Dictionary
Oil Tree. (Hebrew, ets shemen). The Hebrew words occur in Nehemiah 8:15. (Authorized Version, "pine branches"), 1 Kings 6:23, ("olive tree"), and in Isaiah 41:19. ("oil tree").
From the passage in Nehemiah, where the ets shemen is mentioned as distinct from the olive tree, if may perhaps be identified with the zackum tree of the Arabs, the Balanites aegyptiaca, a well-known and abundant shrub, or small tree, in the plain of Jordan. The zackum oil is held in high repute by the Arabs, for its medicinal properties. See Olive.
These files are public domain.
Smith, William, Dr. Entry for 'Oil Tree'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/o/oil-tree.html. 1901.