Agent losing yen for a health resort (3)
I believe the answer is:
spa
'health resort' is the definition.
(thesaurus)
'agent losing yen for a' is the wordplay.
'agent' becomes 'spy' (spy is a kind of agent).
'losing' suggests deleting specific letters.
'yen' becomes 'y'.
'for' means one lot of letters go next to another.
'spy' with 'y' taken out is 'sp'.
'sp'+'a'='SPA'
(Other definitions for spa that I've seen before include "Watering place" , "Cheltenham or Bath?" , "where health benefits are offered" , "Health and beauty treatment establishment" , "Bath, possibly" .)