Abarim Publications' online Biblical Hebrew Dictionary
There are a few different words that are spelled אח ('h). They come from different roots and mean different things.
The noun אח ('ah), means brother. Its proper plural is אחים and its construct form is אחי (brother(s) of). Occasionally, our word occurs in singular while multiple brothers are implied (Genesis 31:37, 37:16), in which case our word denotes brotherhood (which in the Old Testament denotes one's actual brothers). Variations of the term איש אל־אחיו — which literally means 'a man unto his brothers' — are commonly interpreted as 'one onto another' (Leviticus 26:37, 2 Kings 7:6, Ezekiel 24:23).
The origins of this important word אח ('h) are unknown; scholars suggest all kinds of possibilities but all are guessing and none guesses something original enough to warrant reproduction. BDB Theological Dictionary emphasizes, "In many cases however, the meaning of proper names comp. with אח ('ah) is dubious, and perfect consistency, especially in comparison with compounds of אב ('ab), seems impossible". Less elaborate: We simply don't know where, in a literary sense, the Biblical concept of brotherhood comes from.
Obviously kindred words are:
- אחוה ('ahawa), meaning brotherhood. Note that this noun is spelled identical to and pronounced nearly the same as the noun אחוה ('ahwah), meaning declaration, from the verb חוה (hawa II) meaning to show, tell, make known.
- אחות ('ahot), meaning sister.
The word אח ('ah) meaning brother is used, obviously, to indicate a male child of one's parents, or one's mother, other than oneself. But it's also used to indicate "kinship" with the following:
- A more distant relative. In Genesis 13:8 Abraham declares himself and his nephew Lot to be brothers, and in Genesis 29:13-15 Laban and Jacob to the same.
- An even more distant relative. In Numbers 16:10 Moses tells Korah that all the sons of Levi are brothers. In Exodus 2:11, all Israelites are called brothers. Leviticus 19:17 equates countrymen with brothers.
- Related countries: Israel and Judah (2 Samuel 19:42), Israel and Edom (Numbers 20:14).
- A friend (2 Samuel 1:26, 1 Kings 19:13), or an ally (Amos 1:9).
- A figure of resemblance: brother of the jackals (Job 30:29), brother of destruction (Proverbs 18:9).
- In the phrase איש אחיו ('ys 'hyw), literally meaning a man's brother (Genesis 9:5, Joshua 2:8).
The word אח ('ah) often occurs in names with a yod-extension: אחי ('ahi), may mean my brother, brother(s) of or brotherly.
Another word of this same form is אח ('ah); the exclamation of grief, as used in Ezekiel 6:11 and 21:15: Ach! Alas! It's similarly unclear where this word comes from, but perhaps its origin is comparable to the mechanism that gave modern English the exclamation 'O brother!'
There are two separate roots of the form אחח ('hh) in the Bible, but neither is used enough to judge whether they have anything to do with each other:
The root אחח ('hh I) may be onomatopoeic and is comparable to an Arabic verb meaning to cry or howl. In the Bible only one derivation exists: the masculine noun אח ('oah). This word occurs only in Isaiah 13:21 (in the plural אחים), and while it probably denotes some animal, it's unknown which one precisely and the guesses among translators vary widely. To the Hebrew ear, however, this animal was known as 'brother'. Perhaps this animal showed a signature 'brotherly love' and operated in close packs, like a canine.
The root אחח ('hh II) is of unclear meaning or connection to cognate languages. Its sole Biblical derivative is אח ('ah), meaning fire-pot (Jeremiah 36:22-23 only). To the Hebrews this word may have denoted a devise that kept one warm and safe, much alike a brother would.