Legal excuse (5)
I believe the answer is:
alibi
'legal excuse' 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 "Legal term from the Latin 'elsewhere'" , "Evidence of (or excuse for) being somewhere else at the time" , "Making excuse" , "Reason often given to exculpate someone" , "Proof of not being at crime site" .)