Joint account's closing in difficult situation (5)
I believe the answer is:
mitre
'joint' is the definition.
(mitre joint is a kind of joint)
'account's closing in difficult situation' is the wordplay.
'closing' suggests the final letters (the letter which ends or closes the word).
'in' indicates putting letters inside.
'difficult situation' becomes 'mire'.
The last letter of 'account' is 't'.
't' going into 'mire' is 'MITRE'.
(Other definitions for mitre that I've seen before include "What a bishop may have on" , "episcopal head may come under this" , "One identifies bishop" , "symbol of ecclesiastical authority" , "A bishop wears it" .)