Archaic KJV Word
Travail
Modern equivalent: agonizing labor
What Was Lost
The productive agony. Isaiah 53:11 says the Messiah will see the result of His soul's travail and be satisfied -- His suffering was labor that produced something. Like a mother in travail, the agony had a purpose and an outcome. When travail became just 'travel,' the theology of redemptive suffering lost its vocabulary of painful-but-productive labor.
Closest Survivor in Modern English
travail (still used in 'labor and travail' but sounds archaic to most readers)
Peak Usage (1611)
KJV Isaiah 53:11 -- 'He shall see of the travail of his soul, and shall be satisfied'; Galatians 4:19 -- 'My little children, of whom I travail in birth again'
Died ~1900
Collapsed into 'travel' (both from Old French travaillier 'to labor hard'). The split hid the connection between painful labor and journeying -- originally the same word because travel was travail.
What Replaced It
“labor”
Generic work; travail meant agonizing, painful, birth-like labor -- the worst kind of work
“suffering”
Passive endurance; travail was active labor through suffering toward a productive end
“childbirth pain”
Reduces the metaphor; travail was any productive agony, with childbirth as the archetype