Archaic KJV Word
Seed
Modern equivalent: something you plant
What Was Lost
The promise-bearing lineage. 'Her seed' in Genesis 3:15 was the first prophecy of Christ -- the offspring who would crush the serpent's head. Paul argued in Galatians that 'seed' was singular, pointing to Christ. The entire Old Testament narrative tracked the seed from Adam through Abraham through David to Jesus. One unbroken line carrying the promise.
Closest Survivor in Modern English
seed (still used in parables but the covenant-lineage, promise-bearing dimension is agricultural now)
Peak Usage (1611)
KJV Genesis 3:15 -- 'I will put enmity between thy seed and her seed'; Galatians 3:16 -- 'He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ'
Died still used but botanical-ized (~1800)
Hebrew zera ('offspring/descendants/the living continuation of a person through their children/the line through which God's promise travels') was botanicalized into 'what you plant in dirt.' The living, generational, promissory dimension was lost.
What Replaced It
“offspring”
Biological; zera was the chosen line through which God's covenant promise traveled across generations
“descendants”
Genealogical; seed was specifically the promise-bearing line -- not all descendants but the one through whom blessing came
“children”
Familial; seed was theological -- the line that carried God's plan from Abraham to Christ