A saucy upstart about to find opening (8)
I believe the answer is:
aperture
'opening' is the definition.
(aperture is a kind of opening)
'a saucy upstart about' is the wordplay.
'saucy' becomes 'pert' (synonyms).
'upstart' becomes 'u' (start of the word 'up').
'about' becomes 're' ('re' means regarding or about).
'a'+'pert'+'u'+'re'='APERTURE'
'to find' is the link.
(Other definitions for aperture that I've seen before include "Opening (for a photographer?)" , "Small hole or opening" , "Opening through which light enters a camera" , "Device controlling amount of light admitted" , "'Hole, opening (8)'" .)