Suspect's defense (5)
I believe the answer is:
alibi
'suspect's defense' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alibi that I've seen before include "Suspect's excuse" , "Lawyer's weapon, Latin for 'elsewhere'" , "Defence against charge - was seen elsewhere" , "Evidence one was not present" , "Plea of absence" .)