Cold-blooded killer I call ambitious! (8)
I believe the answer is:
aspiring
'ambitious' is the definition.
('aspiring' can be similar in meaning to 'ambitious')
'cold-blooded killer i call' is the wordplay.
'cold-blooded killer' becomes 'asp' (I've seen this before).
'call' becomes 'ring' ('ring' can be a synonym of 'call').
'asp'+'i'+'ring'='ASPIRING'
(Other definitions for aspiring that I've seen before include "Having a strong desire to achieve something" , "Strongly desiring to achieve" , "Hoping" , "Having ambition to achieve greater things" , "Ambitious, hopeful" .)