Excuse offered for absenteeism (5)
I believe the answer is:
alibi
'excuse' is the definition.
(excuse given by a suspect in an investigation)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for alibi that I've seen before include "Claim put to court" , "Answer to charge - was somewhere else" , "Timely get-out" , "Defence against charge - was seen elsewhere" , "Defence against accusation - was somewhere else" .)