Archaic KJV Word
Might
Modern equivalent: strength
What Was Lost
The heroic demonstration. Gevurah was not potential strength but strength proven in action -- the might God demonstrated at the Red Sea, at Jericho, against Pharaoh. 'The power of His might' was not abstract omnipotence but demonstrated, witnessed, history-changing divine force.
Closest Survivor in Modern English
might (still used as a noun but far more common as a verb of possibility, drowning the original meaning)
Peak Usage (1611)
KJV Ephesians 6:10 -- 'Be strong in the Lord, and in the power of his might'; Micah 3:8 -- 'I am full of power by the spirit of the Lord, and of judgment, and of might'
Died still used but diluted (~1800)
Hebrew gevurah ('warrior strength/heroic might/the strength demonstrated in battle/God's mighty acts in history') diluted into 'I might go to the store' -- a modal verb expressing possibility rather than overwhelming force.
What Replaced It
“strength”
Generic; gevurah was specifically warrior strength demonstrated in heroic action
“force”
Impersonal; gevurah was personal, heroic, and demonstrated in God's mighty acts of salvation
“capability”
Potential; gevurah was proven in battle -- strength demonstrated, not merely possessed