Wrongly presume to be most important (7)
I believe the answer is:
supreme
'be most important' is the definition.
(I've seen this before)
'wrongly presume' is the wordplay.
'wrongly' is an anagram indicator (I've seen this in other clues).
'presume' anagrammed gives 'SUPREME'.
'to' is the link.
(Other definitions for supreme that I've seen before include "Best of all" , "Unrivalled" , "Highest in authority; rich cream sauce (dish)" , "topmost level" , "creamy dish of chicken perhaps" .)