round-bottom flask vs flask

round-bottom flask and flask both are nouns.

Word	Noun	Adjective	Verb	Adverb
round-bottom flask	Yes	No	No	No
flask	Yes	No	No	No

As nouns, flask is a hypernym of round-bottom flask; that is, flask is a word with a broader meaning than round-bottom flask:

round-bottom flask (noun)	flask (noun)
a spherical flask with a narrow neck	bottle that has a narrow neck
	the quantity a flask will hold