Insincere mate involved with nun (7)
I believe the answer is:
unmeant
'insincere' is the definition.
(I've seen this in another clue)
'mate involved with nun' is the wordplay.
'involved with' is an anagram indicator (involved can mean confusing or complex).
'mate' anagrammed with 'nun' can make 'UNMEANT'.
(Other definitions for unmeant that I've seen before include "accident" , "not intended" , "Accidental" .)