Ginger tough’s hairdo repelled Serpent (5)
I believe the answer is:
adder
'serpent' is the definition.
(type of snake)
'ginger tough's hairdo repelled' is the wordplay.
'ginger' becomes 'red ginger' (red ginger is a kind of ginger).
'tough's hairdo' becomes 'DA' (short for duck's arse haircut).
'repelled' shows that the letters should be reversed in order.
'red'+'da'='redda'
'redda' back-to-front is 'ADDER'.
(Other definitions for adder that I've seen before include "Venomous sort" , "Type of snake" , "Dread (anag)" , "Venomous type" , "1 of 21 [SNAKES]" .)