base rate vs interest rate

base rate and interest rate both are nouns.

Word	Noun	Adjective	Verb	Adverb
base rate	Yes	No	No	No
interest rate	Yes	No	No	No

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

base rate: the interest rate set by the Bank of England for lending to other banks
interest rate: the percentage of a sum of money charged for its use

Other hypernyms of base rate include rate of interest.

base rate (noun)	interest rate (noun)
the interest rate set by the Bank of England for lending to other banks	the percentage of a sum of money charged for its use