From H7013 (qayin, to strike/forge). While primarily known as the name of Adam's firstborn, the underlying word means a spear or lance — a forged weapon. The dual meaning (acquisition and weapon-forging) captures the tragic trajectory of Cain's line: from the joy of 'I have gotten a man from the LORD' (Gen 4:1) to the violence of fratricide and the weapons industry of his descendants.
The etymology itself tells the story of the Fall's consequences. Eve named her son Qayin ('acquisition') in hopeful expectation — perhaps he was the promised seed of Genesis 3:15. Instead, he became a murderer. His descendant Tubal-Cain became the first metalworker, forging weapons (the qayin as spear). The theological trajectory: human ingenuity apart from God inevitably turns creative capacity into destructive capability. The 'way of Cain' (Jude 1:11) becomes a byword for religion without repentance and worship without obedience.