The Hebrew proper name Achi (אֲחִי) simply means "my brother", from the common noun ach (H251, brother). It appears as a personal name in 1 Chronicles. This type of kinship-as-name reflects the ancient Near Eastern practice of expressing covenant bonds and social solidarity through naming.
The Hebrew concept of brotherhood (ach) carries enormous theological and social weight. Brothers were bound by the deepest ties of covenant loyalty — to love, protect, redeem, and stand with one another (Proverbs 17:17; 18:24). The prophets invoke this bond when rebuking Israel for oppressing the poor: the destitute Israelite was still your ach, your brother (Deuteronomy 15:7). Jesus supremely redefines brotherhood: "Whoever does the will of my Father in heaven is my brother and sister" (Matthew 12:50). Spiritual kinship through obedience to God creates a brotherhood deeper than biology.