gassing vs poisoning

gassing and poisoning both are nouns.

Word	Noun	Adjective	Verb	Adverb
gassing	Yes	No	No	No
poisoning	Yes	No	No	No

As nouns, poisoning is a hypernym of gassing; that is, poisoning is a word with a broader meaning than gassing:

gassing: the deliberate act of poisoning some person or animal with gas
poisoning: the act of giving poison to a person or animal with the intent to kill

gassing (noun)	poisoning (noun)
the deliberate act of poisoning some person or animal with gas	the act of giving poison to a person or animal with the intent to kill
the process of interacting with gas	the physiological state produced by a poison or other toxic substance