Subsequent wild fear about trouble starting (5)
I believe the answer is:
after
'subsequent' is the definition.
(I've seen this before)
'wild fear about trouble starting' is the wordplay.
'wild' indicates an anagram.
'about' is an insertion indicator.
'starting' says to take the initial letters.
The initial letter of 'trouble' is 't'.
'fear' anagrammed gives 'afer'.
'afer' placed around 't' is 'AFTER'.
(Other definitions for after that I've seen before include "Coming later in time" , "In the time following" , "At a later time or behind" , "Behind; in quest of" , "Post, later than" .)