Clear estimate follows former one (9)
I believe the answer is:
exonerate
'clear' is the definition.
(I know that clear can be written as exonerate)
'estimate follows former one' is the wordplay.
'estimate' becomes 'rate' (I've seen this before).
'follows' says to put letters next to each other.
'former' becomes 'ex' (prefix meaning former or onetime).
'ex'+'one'='exone'
'rate' put after 'exone' is 'EXONERATE'.
(Other definitions for exonerate that I've seen before include "Declare to be free from blame" , "Excuse" , "Officially absolve from blame" , "Pronounce not guilty of a crime" , "Justify" .)