Abarim Publications' online Biblical Hebrew Dictionary
There are two roots רחם (rhm), and it's unclear to which extent they have to do with each other:
The meaning of the root רחם (raham) was lost over time, but in cognate language it has meanings varying from to be soft or gentle to being compassionate and affectionate. In the Bible the verb רחם (raham) means to love deeply or have mercy. HAW Theological Wordbook of the Old Testament adds the distinction that this verb usually applies to the affection of a "superior" to an "inferior".
The prophet Isaiah uses it to reflect the love that a mother feels for her baby (Isaiah 49:15). King David uses it for the love that a father has for his child (Psalm 103:13). Very often this verb is used to describe the love or mercy God has for his people (Exodus 33:19, 2 Kings 13:23).
This verb is denominative, which means that it came from a noun (while in Hebrew nouns usually come from verbs). The parent noun of our verb is the masculine רחם (rhm; pronounced as rehem or raham), meaning womb (Genesis 49:25, Exodus 13:12, Jeremiah 20:17). This word may also be used to indicate a woman, presumably in her role as child bearer: Judges 5:30. BDB Theological Dictionary submits that according to "many", the link between loving deeply and the word for womb originates in feelings of fraternal unity, but it may very well have originated somewhere on the vast spectrum of feelings that a man may have for his woman.
Other derivatives are:
- The masculine plural noun רחמים (rahamim), meaning compassions or tender mercies (Genesis 43:30, Isaiah 63:7). The plural form serves as an intensive, and this word is usually employed to describe God's feelings towards man.
- The adjective רחום (rahum), meaning compassionate (Exodus 34:6, Deuteronomy 4:31). This word is always used for God's feelings towards man.
- The adjective רחמני (rahamani), denoting compassionate women (Lamentations 4:10 only).
The meaning of root רחם (raham II) is also missing in action. It occurs in other languages but it's not clear whether these words are truly distinct from root raham I. The Bible contains two derivatives of this root, and each occurs only once, and in the same list of unclean birds:
- The masculine noun רחם (raham), denoting a kind of vulture (Leviticus 11:18).
- The masculine noun רחמה (rahama), denoting the exact same animal in Deuteronomy 14:17.
It's unclear where these words come from, but to a Hebrew audience, these birds were doubtlessly known as love-birds. And this may have made perfect sense from observing the parents care for their chicks.