Mike's spoken message (5)
I believe the answer is:
moral
'message' is the definition.
(moral is a kind of message)
'mike's spoken' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'spoken' becomes 'oral' (similar in meaning).
'm'+'oral'='MORAL'
(Other definitions for moral that I've seen before include "Relating to principles of right and wrong" , "Relating to good and evil" , "Righteous" , "Upright; message of fable" , "Virtuous and principled" .)