flow rate vs rate

flow rate and rate both are nouns.

Word	Noun	Adjective	Verb	Adverb
flow rate	Yes	No	No	No
rate	Yes	No	Yes	No

As nouns, rate is a hypernym of flow rate; that is, rate is a word with a broader meaning than flow rate:

flow rate (noun)	rate (noun)
the amount of fluid that flows in a given time	the relative speed of progress or change
	amount of a charge or payment relative to some basis
	a quantity or amount or measure considered as a proportion of another quantity or amount or measure
	a magnitude or frequency relative to a time unit

flow rate (verb)	rate (verb)
	assign a rank or rating to
	estimate the value of
	be worthy of or have a certain rating