In future, somehow fear going in there, trembling (9)
I believe the answer is:
hereafter
'in future' is the definition.
(I've seen this before)
'somehow fear going in there trembling' is the wordplay.
'somehow' indicates an anagram.
'going in' is an insertion indicator.
'trembling' indicates an anagram.
'fear' anagrammed gives 'reaf'.
'there' with letters rearranged gives 'heter'.
'reaf' put inside 'heter' is 'HEREAFTER'.
(Other definitions for hereafter that I've seen before include "Hence" , "Life in the future" , "In subsequent parts of legal document" .)