A snare set up independently (5)
I believe the answer is:
apart
'independently' is the definition.
(I've seen this in another clue)
'a snare set up' is the wordplay.
'snare' becomes 'trap' (synonyms).
'set up' says the letters should be written backwards (in a down clue, letters go up).
'trap' reversed gives 'part'.
'a'+'part'='APART'
(Other definitions for apart that I've seen before include "in bits" , "Asunder" , "in isolation" , "Separated physically" , "Separated or at a distance" .)