Abarim Publications' online Biblical Hebrew Dictionary
There are two separate verbs רבב (rabab) and two verbs רבה (raba), which are obviously related in form and somewhat adjacent in meaning.
Note the similarity in meaning between this root cluster and the verb כבר (kabar), meaning to be much or many:
The verb רבב (rabab I) means to be or become many (Genesis 6:1, Exodus 23:29). This verb is rarer than the similar verb רבה (raba; see below) and is most often used to describe multitudinous human or animal populations.
This verb's derivatives are:
- The adjective רב (rab I) means much, many or great (Genesis 24:25, Psalm 19:11).
- The identical masculine noun רב (rab II) means chief or captain (= of many — Esther 1:8, Jeremiah 39:3).
- The masculine noun רב (rob) means multitude or abundance (Genesis 16:10, Hosea 8:12).
- The feminine noun רבבה (rebaba) means ten-thousand or myriad (Genesis 24:60, Micah 6:7).
- The later, Aramaized feminine noun רבו (ribo) or רבוא (ribo') also means ten-thousand or myriad (Jonah 4:11, Ezra 2:64).
- The masculine noun רביבים (rebibim) denotes copious showers (Jeremiah 3:3, Psalm 65:10).
The verb רבב (rabab II), means to shoot (Genesis 49:23, Psalm 18:15), and its derived masculine noun רב (rab III) means archer (Jeremiah 50:29, Job 16:13). None of the sources reports a connection between rabab I and II, but apart from the words being the same, a hefty rain shower is not all that different from an attack by a contingent of archers, and if possibly these words evolved from separate ideas into similar forms, this may have happened so readily because they express highly similar images.
The verb רבה (raba I) is similar to רבב (rabab I) and means to be or become great, many, much or numerous. Its antonym is the verb מעט (ma'at), meaning to be or become small, and it's used to mean to increase in number or rather to multiply (Genesis 7:17), or to gather much (Exodus 16:18), to give much (Numbers 26:54), and even to live long (Job 29:18) or to produce much (big) words, i.e. to brag (Job 34:37).
This verb's derivatives are:
- The masculine noun ארבה (arbeh), denoting a kind of locust (Judges 6:5). Note that this word is spelled the same as ארבה ('orba), meaning trickery, and ארבה ('aruba), meaning window or sluice, from the root ארב ('arab).
- The masculine noun מרבה (marbeh), meaning increase (Isaiah 9:6) or abundance (Isaiah 33:23).
- The feminine noun מרבה (mirbah), meaning much (Ezekiel 23:32 only - "much to contain").
- The feminine noun מרבית (marbit), meaning increase, greatness, multitude (1 Samuel 2:33, 2 Chronicles 9:6).
- The feminine noun תרבות (tarbut), meaning increase, brood (Numbers 32:14 only).
- The feminine noun תרבית (tarbit), meaning increment, usury (Ezekiel 18:8).
The verb רבה (raba II) also means to shoot and is used in Genesis 21:20 only. HAW Theological Wordbook of the Old Testament generously offers that this verb is "doubtless a by-form of רבב (rabab II)".