Priest in labour exchange initially upset (3)
I believe the answer is:
eli
'priest' is the definition.
(biblical figure)
'in labour exchange initially upset' is the wordplay.
'initially' indicates taking the first letters.
'upset' says the letters should be written in reverse.
The initial letters of 'in labour exchange' is 'ile'.
'ile' reversed gives 'ELI'.
(Other definitions for eli that I've seen before include "Distort then untruth to get a Biblical character" , "- Whitney invented the cotton gin in seventeen ninety three" , "Priest at Shiloh (Samuel)" , "- Wallach, US actor" , "Shiloh priest (Bible)" .)