Skin headless fish (3)
I believe the answer is:
eel
'fish' is the definition.
(eel is a kind of fish)
'skin headless' is the wordplay.
'skin' becomes 'peel' ('peel' can be a synonym of 'skin').
'headless' means to remove the first letter.
'peel' with its first letter taken off is 'EEL'.
(Other definitions for eel that I've seen before include "Slippery swimmer (may be jellied)" , "Slippery figure" , "Ribbon-like fish" , "Slippery character" , "Large elver" .)