Puts dressing gown out lengthwise (8)
I believe the answer is:
longways
'lengthwise' is the definition.
(synonyms)
'puts dressing gown out' is the wordplay.
'puts' becomes 'lays' (laying is a kind of putting).
'dressing' means one lot of letters goes inside another (inserted letters are dressed or clad in others).
'out' indicates an anagram (out can mean wrong or inaccurate).
'gown' is an anagram of 'ongw'.
'lays' going around 'ongw' is 'LONGWAYS'.
(Other definitions for longways that I've seen before include "Along the length" , "end to end" , "extension of this kind" .)