Certain it somehow became complicated (9)
I believe the answer is:
intricate
'complicated' is the definition.
(I've seen this in another clue)
'certain it somehow' is the wordplay.
'somehow' is an anagram indicator.
'certain'+'it'='certainit'
'certainit' with letters rearranged gives 'INTRICATE'.
'became' is the link.
(Other definitions for intricate that I've seen before include "Convoluted" , "ornate" , "Complicated, detailed" , "Entangled" , "Complex, labyrinthine" .)