Leading lady cut short with smack (6)
I believe the answer is:
heroin
'smack' is the definition.
('heroin' can be a synonym of 'smack')
'leading lady cut short' is the wordplay.
'leading lady' becomes 'heroine' (I've seen this before).
'cut short' means to remove the last letter.
'heroine' with its final letter removed is 'HEROIN'.
'with' acts as a link.
(Other definitions for heroin that I've seen before include "Narcotic powder derived from morphine" , "Class A drug" , "Highly addictive drug madefrom morphine" , "Highly addictive illegal drug" , "Addictive drug sold by pushers" .)