killing zone vs kill zone

killing zone and kill zone both are nouns.

Word	Noun	Adjective	Verb	Adverb
killing zone	Yes	No	No	No
kill zone	Yes	No	No	No

As nouns, killing zone and kill zone are synonyms defined as:

killing zone and kill zone: an area where a battle has occurred with many fatalities

killing zone (noun)	kill zone (noun)
an area where a battle has occurred with many fatalities	an area where a battle has occurred with many fatalities