American painter's short pipe (7)
I believe the answer is:
whistle
'pipe' is the definition.
(I know that whistle is a type of fipple flute)
'american painter's short' is the wordplay.
'american painter' becomes 'whistler' (painter James McNeill Whistler).
'short' means to remove the last letter.
'whistler' with its last letter removed is 'WHISTLE'.
(Other definitions for whistle that I've seen before include "something needing wetting?" , "Become an informer" , "Simple fipple flute" , "He wilts (anag.)" , "Musical with Hayley Mills" .)