Spy sabre, exotic, for witness? (6-2)
I believe the answer is:
passer-by
'witness?' is the definition.
(I've seen this before)
'spy sabre exotic' is the subsidiary indication.
'exotic' indicates an anagram.
'spy'+'sabre'='spysabre'
'spysabre' anagrammed gives 'passerby'.
'for' is the link.
(Other definitions for passer-by that I've seen before include "One happening past" , "One walking near" , "Person who happens to be going past" , "Witness" , "Spectator not stopping?" .)