Easton's Bible Dictionary
(1.) Hebrews bik'ah, a "cleft" of the mountains (Deuteronomy 8:7; 11:11; Psalm 104:8; Isaiah 41:18); also a low plain bounded by mountains, as the plain of Lebanon at the foot of Hermon around the sources of the Jordan (Joshua 11:17; 12:7), and the valley of Megiddo (2 Chronicles 35:22).
(2.) `Emek, "deep;" "a long, low plain" (Job 39:10, 21; Psalm 65:13; Cant. 2:1), such as the plain of Esdraelon; the "valley of giants" (Joshua 15:8), usually translated "valley of Rephaim" (2 Samuel 5:18); of Elah (1 Samuel 17:2), of Berachah (2 Chronicles 20:26); the king's "dale" (Genesis 14:17); of Jehoshaphat (Joel 3:2, 12), of Achor (Joshua 7:24; Isaiah 65:10), Succoth (Psalm 60:6), Ajalon (Joshua 10:12), Jezreel (Hosea 1:5).
The "valley of vision" (Isaiah 22:1) is usually regarded as denoting Jerusalem, which "may be so called," says Barnes (Com. on Isaiah), "either (1) because there were several valleys within the city and adjacent to it, as the vale between Mount Zion and Moriah, the vale between Mount Moriah and Mount Ophel, between these and Mount Bezetha, and the valley of Jehoshaphat, the valley of the brook Kidron, etc., without the walls of the city; or (2) more probably it was called the valley in reference to its being compassed with hills rising to a considerable elevation above the city" (Psalm 125:2; Comp. also Jeremiah 21:13, where Jerusalem is called a "valley").
(4.) Hebrews nahal, a wady or water-course (Genesis 26:19; Cant. 6:11).
Noah Webster's New International Dictionary of the English Language
1. (n.) The space enclosed between ranges of hills or mountains; the strip of land at the bottom of the depressions intersecting a country, including usually the bed of a stream, with frequently broad alluvial plains on one or both sides of the stream. Also used figuratively.
2. (n.) The place of meeting of two slopes of a roof, which have their plates running in different directions, and form on the plan a reentrant angle.
3. (n.) The depression formed by the meeting of two slopes on a flat roof.