Request one’s placed between wife and husband (4)
I believe the answer is:
wish
'request' is the definition.
(wish is a kind of request)
'one's placed between wife and husband' is the wordplay.
'one's' becomes 'is' (Roman numeral**).
'placed between' indicates putting letters inside.
'wife' becomes 'w'.
'and' says to put letters next to each other.
'husband' becomes 'h'.
'w'+'h'='wh'
'is' going within 'wh' is 'WISH'.
(Other definitions for wish that I've seen before include "Desire, hope" , "prayer" , "whim" , "Express a desire (upon a star?)" , "Desire (to pull this bone?)" .)