Stop dead and liberate heartless zombie (6)
I believe the answer is:
freeze
'stop dead' is the definition.
(I know that stop dead can be written as freeze)
'liberate heartless zombie' is the wordplay.
'liberate' becomes 'free' (synonyms).
'heartless' suggests removing the centre.
'zombie' with its middle removed is 'ze'.
'free'+'ze'='FREEZE'
'and' is the link.
(Other definitions for freeze that I've seen before include "period of cold weather" , "Change to ice" , "Hold at fixed level - say prices" , "Change liquid to solid through cooling" , "Don't move!" .)