Article impounded by prudish Trojan king (5)
I believe the answer is:
priam
'trojan king' is the definition.
(king of Troy in Greek mythology)
'article impounded by prudish' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'impounded by' indicates putting letters inside.
'prudish' becomes 'prim' (synonyms).
'a' placed into 'prim' is 'PRIAM'.
(Other definitions for priam that I've seen before include "Old man of Paris" , "Father of Paris in Troy" , "Ruler of Troy" , "The last king of Troy, in Greek mythology" , "Old king" .)