Abarim Publications' online Biblical Hebrew Dictionary
The root-verb להב (lhb) isn't used in the Bible but in cognate languages it occurs with meanings that all have to do with fire and burning. But this root must have existed, even though none of the Bible writers happened to use it, because three derivatives appear quite regularly:
- The masculine noun להב (lahab), meaning flame (Judges 13:20, Isaiah 29:6). This word may also denote the blade of a sword (Nahum 3:3) or the tip of a spear (Job 39:23), but it isn't clear how the connection works. Is it because light flashed off these weapons, as BDB Theological Dictionary proposes? Probably not because those implements at that time weren't very shiny. Perhaps it was because swords and spears were shaped like little flames. But in Hebrew nouns usually come from verbs, which means that things were usually known not for their shape but for some kind of action (see our awesome article To Be Is To Do). In the case of these weapons, that action is probably the process by which they were made: through fire. In fact, the art of making a fire hotter was directly tied in to the art of making your metals purer, which meant the art of making your weapons stronger. The hotter your fire, the stronger your military force, and the greater your chances of survival. In fact, the relation between fire, wisdom and life is quite obviously explored in the Bible.
- The feminine equivalent להבה (lehaba), also means flame or blade but tends to be used in much more poetic contexts — flame of conquest: Numbers 21:28; flame of anger: Hosea 7:6; the flame of God's judgment: Isaiah 5:24.
- The feminine noun שלהבת (shalhebet), also meaning flame and also used poetically (Job 15:30, Song of Solomon 8:6).
Also note that the somewhat similar noun לב (leb) means heart.