Quick to grab a knife (7)
I believe the answer is:
cleaver
'knife' is the definition.
(I know that cleaver is a type of knife)
'quick to grab a' is the wordplay.
'quick' becomes 'clever' (synonyms).
'to grab' indicates putting letters inside.
'clever' placed around 'a' is 'CLEAVER'.
(Other definitions for cleaver that I've seen before include "A butcher's chopping tool" , "Butcher's knife" , "A clever sort of axe" , "Butcher's chopper" , "(Meat) chopper" .)