Witch putting rat's head in ice cream (5)
I believe the answer is:
crone
'witch' is the definition.
(synonyms)
'rat's head in ice cream' is the wordplay.
'head' says to take the initial letters.
'in' indicates putting letters inside.
'ice cream' becomes 'cone' (cone can refer to an ice cream cone).
The first letter of 'rats' is 'r'.
'r' inserted into 'cone' is 'CRONE'.
'putting' is the link.
(Other definitions for crone that I've seen before include "old-womanish type" , "withered old woman" , "Ugly old woman" , "Old hag" , "offensive old woman" .)