vacuum flask vs Dewar

vacuum flask and Dewar both are nouns.

Word	Noun	Adjective	Verb	Adverb
vacuum flask	Yes	No	No	No
Dewar	Yes	No	No	No

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

vacuum flask: flask with double walls separated by vacuum; used to maintain substances at high or low temperatures
Dewar: vacuum flask that holds liquid air or helium for scientific experiments

Other hyponyms of vacuum flask include Dewar flask, thermos, thermos bottle, thermos flask.

vacuum flask (noun)	Dewar (noun)
flask with double walls separated by vacuum; used to maintain substances at high or low temperatures	vacuum flask that holds liquid air or helium for scientific experiments
	Scottish chemist and physicist noted for his work in cryogenics and his invention of the Dewar flask (1842-1923)