Abarim Publications' online Biblical Hebrew Dictionary
The root רכב (rakab) has to do with chariots and riding them, and since the chariot was invented in Babylon and the word by which it was known there looks a lot like our verb רכב (rakab), it's generally assumed that he word was imported along with the vehicle.
The verb רכב (rakab) means to mount and by implication to ride, and although this verb is mostly associated with chariots (Genesis 41:43, 1 Kings 18:45, Jeremiah 17:25), it's also used to describe riding a camel (Genesis 24:61), donkeys and mules (1 Samuel 25:42, 2 Samuel 13:29), and horses (Zechariah 1:8).
In its most basic essence, our verb does not so much describe moving around or being transported (riding), but rather a taking control over (driving). In his oracle against Egypt, Isaiah depicts YHWH as riding on a swift cloud, and something comparable is mentioned in Psalm 104:3, where the Lord appoint clouds to be His chariot — using the specially derived noun רכוב (rekub), see below. This obviously doesn't mean that the Lord is bobbing about in the troposphere, but rather that He is driving the clouds. Similarly, the Lord flings Job up in the air to be driven around by the wind (Job 30:22; most translations have Job "ride" the wind, but that makes no sense). The Psalmist observes that the Lord had men drive his people around (Psalm 66:12); through Hosea He declares that He will drive Ephraim like a heifer (Hosea 10:11), and Elisha taught king Joash a lesson or two about driving an army ("the chariots of Israel and its horsemen") by having him drive a bow (2 Kings 13:16; and not let his hand "ride" the bow, as some interpreters suggest).
The derived masculine noun רכב (rekeb) denotes something driven. This noun is mostly used to describe chariots: those of Egypt (Genesis 46:29), which were destroyed in the Sea of Reeds (Exodus 14:9); those of the Canaanite alliance (Joshua 11:4), which were destroyed at the waters of Merom (Joshua 11:5, 11:9); those of king Jabin and his general Sisera (Judges 4:3), which were destroyed at mount Tabor (Judges 4:16); and those of king Hadadezer of Zobah, which king David captured and put to use in his own army (2 Samuel 8:4). David had only a hundred chariots, but the Lord has myriads (Psalm 68:17, 2 Kings 6:17).
Possibly the most spectacular chariot to occur in the Bible is Elijah's chariot of fire (רכב־אש), partly because it's one of the most spectacularly misrepresented phenomena of the Scriptures (2 Kings 2:11). Whatever it was, it was accompanied by horses of fire (סוס אש) but not necessarily drawn by them. It was probably also not one chariot, because the singular noun רכב (rekeb) is used most often to describe chariotry (that's cavalry with chariots), whereas the feminine noun מרכבה (merkaba) describes one chariot. Elijah also didn't board it to zip off to heaven in it, as the song goes; the fiery chariotry and horses merely separated Elijah from Elisha, and Elijah went to heaven in a whirlwind. The fiery chariotry was also not a UFO but "the chariots and horses of Israel" (2 Kings 2:12), probably the same ones Elisha showed his unnamed servant (not Gehazi) on the mountain (2 Kings 6:17), and those who were readied at the disposal of Jesus (Matthew 26:53).
But our noun רכב (rekeb) is also used to describe a part of a grinder, namely the mobile round stone that was driven along a stationary circular base in order to turn grain into flour. This item was so crucial to every day life that it couldn't be used as a pledge (Deuteronomy 24:6), but it came in awfully handy if someone needed to be killed from above (as in the case of Abimelech of Shechem; Judges 9:53, 2 Samuel 11:21).
Other derivations are:
- The feminine noun רבכה (rikba), meaning a driving (Ezekiel 27:20 only).
- The masculine noun רכב (rakkab), meaning a driver (1 Kings 22:34 = 2 Chronicles 18:23 and 2 Kings 9:17 only).
- The masculine noun רכוב (rekub), meaning (God's) chariot (Psalm 104:3 only).
- The masculine noun מרכב (merkab), literally "place/thing of driving". It occurs three times and denotes a seat or saddle (Leviticus 15:9, Song of Solomon 3:10), or chariotry as physical thing (as opposed to a force in battle; 1 Kings 4:26).
- The feminine noun מרכבה (markaba), denoting a single chariot (Exodus 14:25, 1 Kings 10:29, Micah 5:10).