One minute lesson is corrupt (7)
I believe the answer is:
immoral
'is corrupt' is the definition.
(similar in meaning)
'one minute lesson' is the wordplay.
'one' becomes 'I' (Roman numeral).
'minute' becomes 'm' (abbreviation).
'lesson' becomes 'moral' (as in the moral of the story).
'i'+'m'+'moral'='IMMORAL'
(Other definitions for immoral that I've seen before include "Not conforming to accepted rules of conduct, particularly in sexual matters" , "Evil" , "Unprincipled or debauched" , "Abandoned" , "bad!" .)