Gap or hiatus (6)
I believe the answer is:
lacuna
I believe this clue is a double definition.
'gap' is the first definition.
(I know that lacuna is a type of gap)
'hiatus' is the second definition.
(I've seen this in another clue)
(Other definitions for lacuna that I've seen before include "Gap or hiatus" , "Hiatus - cavity" , "Blank gap or missing part" , "Gap or missing portion" , "Space in book or manuscript" .)