poisoning vs gassing

poisoning and gassing both are nouns.

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

As nouns, gassing is a hyponym of poisoning; that is, gassing is a word with a more specific, narrower meaning than poisoning:

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

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