My asp slithered around Japanese Australian’s nightdress (7)
I believe the answer is:
pyjamas
'nightdress' is the definition.
(both are worn in bed)
'my asp slithered around japanese australian's' is the wordplay.
'slithered' indicates an anagram.
'around' means one lot of letters goes inside another.
'japanese' becomes 'j' (international code for Japanese vehicles).
'australian' becomes 'a'.
'my'+'asp'='myasp'
'myasp' is an anagram of 'pymas'.
'j'+'a'='ja'
'pymas' placed around 'ja' is 'PYJAMAS'.
(Other definitions for pyjamas that I've seen before include "Night attire" , "Sleeping-suit" , "Pays Maj poorly to wear them" , "Jam a spy into these at night" , "Nightwear" .)