A saucy virgin doesn't open mouth (8)
I believe the answer is:
aperture
'mouth' is the definition.
(thesaurus)
'a saucy virgin doesn't open' is the wordplay.
'saucy' becomes 'pert' (synonyms).
'virgin' becomes 'pure' (synonyms).
'doesn't open' means to remove the first letter.
'pure' with its initial letter removed is 'ure'.
'a'+'pert'+'ure'='APERTURE'
(Other definitions for aperture that I've seen before include "Small hole or opening" , "Crack" , "Hole, gap" , "Opening, to let light enter a camera perhaps" , "Opening (for a photographer?)" .)