Superlatively clever as an anagram for instance? (8)
I believe the answer is:
canniest
'superlatively clever' is the definition.
'an anagram for instance?' is the wordplay.
'an anagram for' indicates anagramming the letters.
'instance' with letters rearranged gives 'CANNIEST'.
'as' acts as a link.
(Other definitions for canniest that I've seen before include "Instance (anag)" , "Shrewdest sort of ancients" .)