airing vs propagation

airing and propagation both are nouns.

Word	Noun	Adjective	Verb	Adverb
airing	Yes	No	No	No
propagation	Yes	No	No	No

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

airing: the opening of a subject to widespread discussion and debate
propagation: the spreading of something (a belief or practice) into new regions

Other hyponyms of airing include circulation, extension.

airing (noun)	propagation (noun)
the act of supplying fresh air and getting rid of foul air	the act of producing offspring or multiplying by such production
a short excursion (a walk or ride) in the open air	the spreading of something (a belief or practice) into new regions
the opening of a subject to widespread discussion and debate	the movement of a wave through a medium