Proper to accommodate a Trojan king (5)
I believe the answer is:
priam
'trojan king' is the definition.
(I've seen this before)
'proper to accommodate a' is the wordplay.
'proper' becomes 'prim' ('prim' can be similar in meaning to 'proper').
'to accommodate' indicates putting letters inside.
'prim' placed around 'a' is 'PRIAM'.
(Other definitions for priam that I've seen before include "The last king of Troy, in Greek mythology" , "Old man of Paris" , "Trojan king" , "Ruler of Troy" , "Old king" .)