Easton's Bible Dictionary
There are six Hebrew words rendered "oak."
(1.) `El occurs only in the word El-paran (Genesis 14:6). The LXX. renders by "terebinth." In the plural form this word occurs in Isaiah 1:29; 57:5 (A.V. marg. and R.V., "among the oaks"); 61:3 ("trees"). The word properly means strongly, mighty, and hence a strong tree.
(2.) `Elah, Genesis 35:4, "under the oak which was by Shechem" (R.V. marg., "terebinth"). Isaiah 6:13, A.V., "teil-tree;" R.V., "terebinth." Isaiah 1:30, R.V. marg., "terebinth." Absalom in his flight was caught in the branches of a "great oak" (2 Samuel 18:9; R.V. marg., "terebinth").
(4.) `Elan, only in Dan. 4:11,14,20, rendered "tree" in Nebuchadnezzar's dream. Probably some species of the oak is intended.
(6.) `Allon, always rendered "oak." Probably the evergreen oak (called also ilex and holm oak) is intended. The oak woods of Bashan are frequently alluded to (Isaiah 2:13; Ezek. 27:6). Three species of oaks are found in Palestine, of which the "prickly evergreen oak" (Quercus coccifera) is the most abundant. "It covers the rocky hills of Palestine with a dense brushwood of trees from 8 to 12 feet high, branching from the base, thickly covered with small evergreen rigid leaves, and bearing acorns copiously." The so-called Abraham's oak at Hebron is of this species. Tristram says that this oak near Hebron "has for several centuries taken the place of the once renowned terebinth which Marked the site of Mamre on the other side of the city. The terebinth existed at Mamre in the time of Vespasian, and under it the captive Jews were sold as slaves. It disappeared about A.D. 330, and no tree now Marks the grove of Mamre. The present oak is the noblest tree in Southern Palestine, being 23 feet in girth, and the diameter of the foliage, which is unsymmetrical, being about 90 feet." (see HEBRON; TEIL-TREE.)
Noah Webster's New International Dictionary of the English Language
1. (n.) Any tree or shrub of the genus Quercus. The oaks have alternate leaves, often variously lobed, and staminate flowers in catkins. The fruit is a smooth nut, called an acorn, which is more or less enclosed in a scaly involucre called the cup or cupule. There are now recognized about three hundred species, of which nearly fifty occur in the United States, the rest in Europe, Asia, and the other parts of North America, a very few barely reaching the northern parts of South America and Africa. Many of the oaks form forest trees of grand proportions and live many centuries. The wood is usually hard and tough, and provided with conspicuous medullary rays, forming the silver grain.
2. (n.) The strong wood or timber of the oak.