Verification is essential to clause ceding title (5)
I believe the answer is:
audit
'verification' is the definition.
'essential to clause ceding title' is the wordplay.
'essential to' means to look at the middle letters.
'ceding title' becomes 'dit' (I can't explain this - if you can you should believe this answer much more).
The middle letters of 'clause' are 'au'.
'au'+'dit'='AUDIT'
'is' acts as a link.
(Other definitions for audit that I've seen before include "Investigate" , "Inspection of the account books" , "Inspect accounts" , "Thoroughgoing check" , "Financial investigation" .)