Additional trouble avoided by bishop (5)
I believe the answer is:
other
'additional' is the definition.
(I've seen this before)
'trouble avoided by bishop' is the wordplay.
'trouble' becomes 'bother' (synonyms).
'avoided by' suggests deleting specific letters.
'bishop' becomes 'B' (chess abbreviation).
'bother' with 'b' removed is 'OTHER'.
(Other definitions for other that I've seen before include "Alternative of two" , "Remaining" , "Alternative - unrelated" , "Different; alternate" , "else!" .)