From to kill and off.
kill off (third-person singular simple present kills off, present participle killing off, simple past and past participle killed off)
- To eliminate, or make extinct
- We killed off the Dodo by over-hunting.
- The writers are killing off lots of people in the soap opera.
- To put an end to.
2011 September 28, Tom Rostance, “Arsenal 2 - 1 Olympiakos”, BBC Sport:
- Marouane Chamakh then spurned a great chance to kill the game off when he ran onto Andrey Arshavin's lofted through ball but shanked his shot horribly across the face of goal.