departure vs sailing

departure and sailing both are nouns.

Word	Noun	Adjective	Verb	Adverb
departure	Yes	No	No	No
sailing	Yes	No	No	No

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

departure (noun)	sailing (noun)
the act of departing	riding in a sailboat
euphemistic expressions for death	the work of a sailor
a variation that deviates from the standard or norm	the departure of a vessel from a port
	the activity of flying a glider