Vixen less than cunning! (5)
I believe the answer is:
shrew
'vixen' is the definition.
(I've seen this before)
'less than cunning' is the wordplay.
'less than' means to remove the last letter (not the full word).
'cunning' becomes 'shrewd' (I've seen this before).
'shrewd' with its final letter taken off is 'SHREW'.
(Other definitions for shrew that I've seen before include "Scold; insectivore" , "Long-nosed mammal" , "Scold, termagant" , "Mouse-like creature" , "Shakespeare: 'The Taming of the ....'" .)