Wrongly presume it's the highest (7)
I believe the answer is:
supreme
'the highest' is the definition.
(I've seen this in another clue)
'wrongly presume' is the wordplay.
'wrongly' indicates an anagram (I've seen this in other clues).
'presume' with letters rearranged gives 'SUPREME'.
'it's' is the link.
(Other definitions for supreme that I've seen before include "Greatest, highest in excellence" , "Highest in authority; rich cream sauce (dish)" , "Highest in rank - incomparable" , "Unsurpassed" , "Paramount" .)