Where, abroad, one volunteers to finish promptly? (5)
I believe the answer is:
italy
'where abroad' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'one volunteers to finish promptly?' is the wordplay.
'one' becomes 'i' (Roman numeral).
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'to finish promptly?' becomes 'ly' (I can't justify this - if you can you should give a lot more credence to this answer).
'i'+'ta'+'ly'='ITALY'
Can you help me to learn more?
(Other definitions for italy that I've seen before include "Mediterranean nation" , "South European country" , "Europe's boot, home to the Mafia" , "Country shaped like a boot" , "Latin country" .)