Abarim Publications' online Biblical Greek Dictionary
βραχυς
The adjective βραχυς (brachus) means short, the opposite of μακρος (makros), which means long and distant, and an equivalent of μικρος (mikros), which means small or short. Our adjective βραχυς (brachus) stems from the same Proto-Indo-European root "mreg-", short, as the Latin adjective brevis, and thus the English word brief. From the same PIE root comes also the English word merry, curiously demonstrating that our forebears associated comfort and joy with it being over quick (a merry ditty was also a short ditty).
In the classics, our adjective βραχυς (brachus) could describe brevity of space and time (a short while, a short distance), but also of size (a short person, a low wall), quantity (a few words), or quality (of little value or importance). It's used 7 times in the New Testament, see full concordance, and from it comes:
- The noun βραχιων (brachion) meaning arm, or more precise: the upper arm, perhaps plus shoulder (Luke 1:51, John 12:38 and Acts 13:17 only). This word literally means "shorter". It is a comparative of the previous, and was in the classics on occasion indeed used as such. There was also a superlative: βραχιστος (brachistos), shortest, which didn't correspond to a body part, as far as is known.
Why the Greeks dubbed the upper arm "shorter" is not at all clear, and even so confusing that some commentators have demanded that our word βραχιων (brachion), upper arm, is not at all related to βραχυς (brachus), short, and only accidentally looks that way. But the alternative etymology of this new word is subsequently deemed obscure, so this proposal isn't very fruitful. Some say that the upper arm (attached to the shoulder) was named such because it was shorter than the lower arm (with the hand on it). But a quick self-check suggests that this difference is marginal with normally proportioned people. And this word was adopted into Latin, as brachium, where it came to describe the lower or forearm.
Here at Abarim Publications we don't know either, but if we were to guess we'd guess that there was no significant difference in Roman and Greek anatomy, or in the length of forearm and upper arm. Instead, we surmise that arms were called the shorter limbs because legs were longer. Quadrupeds have same-sized front and hind legs but humans have significantly bigger legs than arms.
Significantly, our noun βραχιων (brachion) is used in the New Testament only to describe the "arms" of God. God, of course, has wings (Deuteronomy 32:11, Psalm 17:8, 36:7, 57:1, 61:4, 63:7, 91:4, Jeremiah 49:22).