This will show when undressed (5-4)
I believe the answer is:
roughhewn
'undressed' is the definition.
(thesaurus)
'this will show when' is the wordplay.
I cannot really understand how this works, but
an anagram of 'when' is 'hewn' which is within the answer.
The remaining letters 'rough' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for roughhewn that I've seen before include "Craggy; unrefined" , "(Of wood or stone) not smoothly cut" .)