Rodents having a name for spitefulness (6)
I believe the answer is:
malice
'spitefulness' is the definition.
(synonyms)
'rodents having a name' is the wordplay.
'rodents' becomes 'mice' (mouse is a kind of rodent).
'having' indicates putting letters inside.
'a name' becomes 'al' ().
'mice' enclosing 'al' is 'MALICE'.
'for' acts as a link.
(Other definitions for malice that I've seen before include "Hate" , "Bitterness" , "evil intent" , "Spite - desire to hurt" , "Malevolence, spite" .)