Overcoat for a wan baby (7)
I believe the answer is:
paletot
'overcoat' is the definition.
(I have seen 'large overcoat' mean 'paletot' so perhaps 'overcoat' could also mean 'paletot')
'wan baby' is the wordplay.
'wan' becomes 'pale' (synonyms).
'baby' becomes 'tot' (I've seen this in another clue).
'pale'+'tot'='PALETOT'
'for a' acts as a link.
(Other definitions for paletot that I've seen before include "large overcoat" , "cloak" , "coat" , "loose outer garment" .)