Clever voiding of guarantee, unions I suspect defending it (9)
I believe the answer is:
ingenious
'clever' is the definition.
(ingenious means very clever)
'voiding of guarantee unions i suspect defending it' is the wordplay.
'voiding of' means to remove the middle letters.
'suspect' is an anagram indicator (a suspicious or unusual spelling).
'defending it' is an insertion indicator.
'guarantee' with its middle removed is 'ge'.
'unions'+'i'='unionsi'
'unionsi' with letters rearranged gives 'innious'.
'ge' placed inside 'innious' is 'INGENIOUS'.
(Other definitions for ingenious that I've seen before include "Clever, inventive" , "Brilliant" , "Showing inventiveness" , "Artless" , "Creative" .)