Statement (9)
(Other definitions for assertion that I've seen before include "Confident statement of fact" , "Confident declaration" , "Claim" , "Emphatic declaration" , "Notarises (anag)" .)
'statement' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for utterance that I've seen before include "Expression in speech" , "Statement" , "one's said" , "sermon, say" , "Vocal expression" .)
'statement' is the definition.
(I know that equation is a type of mathematical statement)
This is all the clue.
(Other definitions for equation that I've seen before include "Mathematical statement that two expressions are equal" , "See 5" , "Mathematical relationship" , "E.g. 2 + 2 = 4" , "Statement that two things have the same value" .)