Assist old boy with raincoat going up country (8)
I believe the answer is:
cambodia
'country' is the definition.
(I know that Cambodia is a Asian country)
'assist old boy with raincoat going up' is the wordplay.
'assist' becomes 'aid' (synonyms).
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'with' means one lot of letters go next to another.
'raincoat' becomes 'mac' (macintosh is a type of raincoat).
'going up' says the letters should be written in reverse (in a down clue, the letters are written upwards).
'aid'+'ob'+'mac'='aidobmac'
'aidobmac' back-to-front is 'CAMBODIA'.
(Other definitions for cambodia that I've seen before include "This was formerly Kampuchea" , "Country, part of Indochina under French rule until 1953" , "Country in southeast Asia, home to Khmer people" , "Southeast Asian country" , "Oriental country" .)