First husband exposed by topless minx (4)
I believe the answer is:
adam
'first husband' is the definition.
(Adam was Eve's husband in the Garden of Eden)
'topless minx' is the wordplay.
'topless' means to remove the first letter.
'minx' becomes 'madam'.
'madam' with its first letter taken off is 'ADAM'.
'exposed by' acts as a link.
(Other definitions for adam that I've seen before include "First man of Genesis" , "- - Bede, novel" , "Robert -, Sc. architect" , "__ Smith, author of The Wealth of Nations" , "Biblical first man" .)