With a politician I have such an excuse (5)
I believe the answer is:
alibi
'excuse' is the definition.
(excuse given by a suspect in an investigation)
'with a politician i have such an' is the wordplay.
'with' is an insertion indicator.
'a politician' becomes 'lib'.
'i' becomes 'a'.
'have' says to put letters next to each other.
'such an' becomes 'i' (Roman numeral for one. I am not sure about the 'such' bit.).
'a'+'i'='ai'
'lib' put inside 'ai' is 'ALIBI'.
Can you help me to learn more?
(Other definitions for alibi that I've seen before include "Plea of absence" , "Excuse - plea of being elsewhere" , "Proof of not being at the scene of the crime" , "Timely excuse" , "in order to prove I was elsewhere" .)