Certain it could turn out to be difficult (9)
I believe the answer is:
intricate
'difficult' is the definition.
(thesaurus)
'certain it could turn out to be' is the wordplay.
'could turn out to be' is an anagram indicator.
'certain'+'it'='certainit'
'certainit' with letters rearranged gives 'INTRICATE'.
(Other definitions for intricate that I've seen before include "puzzlingly obscure" , "Very complicated and involved" , "ornate" , "Convoluted" , "Complicated, detailed" .)