Old woman cold in raincoat (3)
I believe the answer is:
mac
'raincoat' is the definition.
(macintosh is a type of raincoat)
'old woman cold' is the wordplay.
'old woman' becomes 'ma' (both can mean someone's mother).
'cold' becomes 'C' (eg on taps).
'ma'+'c'='MAC'
'in' is the link.
(Other definitions for mac that I've seen before include "It may help you keep dry" , "Coat - computer" , "Overcoat" , "A Gaelic son, often in name" , "Waterproof raincoat, in short" .)