flask vs canteen

flask and canteen both are nouns.

Word	Noun	Adjective	Verb	Adverb
flask	Yes	No	No	No
canteen	Yes	No	No	No

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

flask (noun)	canteen (noun)
bottle that has a narrow neck	a flask for carrying water; used by soldiers or travelers
the quantity a flask will hold	restaurant in a factory; where workers can eat
	a recreation room in an institution
	a restaurant outside; often for soldiers or policemen
	sells food and personal items to personnel at an institution or school or camp etc.