assurance vs certainty

assurance and certainty both are nouns.

Word	Noun	Adjective	Verb	Adverb
assurance	Yes	No	No	No
certainty	Yes	No	No	No

As nouns, certainty is a hypernym of assurance; that is, certainty is a word with a broader meaning than assurance:

assurance (noun)	certainty (noun)
freedom from doubt; belief in yourself and your abilities	something that is certain
a statement intended to inspire confidence	the state of being certain
a binding commitment to do or give or refrain from something
a British term for some kinds of insurance